Ubuntu Feisty 7.04 manual page repository

Ubuntu is a free computer operating system based on the Linux kernel. Many IT companies, like DeployIS is using it to provide an up-to-date, stable operating system.

Provided by: libdbi-perl_1.53-1build1_i386

 

NAME

        DBI - Database independent interface for Perl
 

SYNOPSIS

          use DBI;
 
          @driver_names = DBI->available_drivers;
          %drivers      = DBI->installed_drivers;
          @data_sources = DBI->data_sources($driver_name, \%attr);
 
          $dbh = DBI->connect($data_source, $username, $auth, \%attr);
 
          $rv  = $dbh->do($statement);
          $rv  = $dbh->do($statement, \%attr);
          $rv  = $dbh->do($statement, \%attr, @bind_values);
 
          $ary_ref  = $dbh->selectall_arrayref($statement);
          $hash_ref = $dbh->selectall_hashref($statement, $key_field);
 
          $ary_ref  = $dbh->selectcol_arrayref($statement);
          $ary_ref  = $dbh->selectcol_arrayref($statement, \%attr);
 
          @row_ary  = $dbh->selectrow_array($statement);
          $ary_ref  = $dbh->selectrow_arrayref($statement);
          $hash_ref = $dbh->selectrow_hashref($statement);
 
          $sth = $dbh->prepare($statement);
          $sth = $dbh->prepare_cached($statement);
 
          $rc = $sth->bind_param($p_num, $bind_value);
          $rc = $sth->bind_param($p_num, $bind_value, $bind_type);
          $rc = $sth->bind_param($p_num, $bind_value, \%attr);
 
          $rv = $sth->execute;
          $rv = $sth->execute(@bind_values);
          $rv = $sth->execute_array(\%attr, ...);
 
          $rc = $sth->bind_col($col_num, \$col_variable);
          $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
 
          @row_ary  = $sth->fetchrow_array;
          $ary_ref  = $sth->fetchrow_arrayref;
          $hash_ref = $sth->fetchrow_hashref;
 
          $ary_ref  = $sth->fetchall_arrayref;
          $ary_ref  = $sth->fetchall_arrayref( $slice, $max_rows );
 
          $hash_ref = $sth->fetchall_hashref( $key_field );
 
          $rv  = $sth->rows;
 
          $rc  = $dbh->begin_work;
          $rc  = $dbh->commit;
          $rc  = $dbh->rollback;
 
          $quoted_string = $dbh->quote($string);
 
          $rc  = $h->err;
          $str = $h->errstr;
          $rv  = $h->state;
 
          $rc  = $dbh->disconnect;
 
        The synopsis above only lists the major methods and parameters.
 
        GETTING HELP
 
        If you have questions about DBI, or DBD driver modules, you can get
        help from the dbi-users@perl.org mailing list.  You can get help on
        subscribing and using the list by emailing dbi-users-help@perl.org.
 
        To help you make the best use of the dbi-users mailing list, and any
        other lists or forums you may use, I strongly recommend that you read
        "How To Ask Questions The Smart Way" by Eric Raymond:
        <http://www.catb.org/~esr/faqs/smart-questions.html>.
 
        If you think you’ve found a bug then please also read "How to Report
        Bugs Effectively" by Simon Tatham: <http://www.chiark.gree‐
        nend.org.uk/~sgtatham/bugs.html>.
 
        The DBI home page at <http://dbi.perl.org/> is always worth a visit and
        includes an FAQ and links to other resources.
 
        Before asking any questions, reread this document, consult the archives
        and read the DBI FAQ. The archives are listed at the end of this docu‐
        ment and on the DBI home page.  An FAQ is installed as a DBI::FAQ mod‐
        ule so you can read it by executing "perldoc DBI::FAQ".  However the
        DBI::FAQ module is currently (2004) outdated relative to the online FAQ
        on the DBI home page.
 
        This document often uses terms like references, objects, methods.  If
        you’re not familar with those terms then it would be a good idea to
        read at least the following perl manuals first: perlreftut, perldsc,
        perllol, and perlboot.
 
        Please note that Tim Bunce does not maintain the mailing lists or the
        web page (generous volunteers do that).  So please don’t send mail
        directly to him; he just doesn’t have the time to answer questions per‐
        sonally. The dbi-users mailing list has lots of experienced people who
        should be able to help you if you need it. If you do email Tim he’s
        very likely to just forward it to the mailing list.
 
        NOTES
 
        This is the DBI specification that corresponds to the DBI version 1.53.
 
        The DBI is evolving at a steady pace, so it’s good to check that you
        have the latest copy.
 
        The significant user-visible changes in each release are documented in
        the DBI::Changes module so you can read them by executing "perldoc
        DBI::Changes".
 
        Some DBI changes require changes in the drivers, but the drivers can
        take some time to catch up. Newer versions of the DBI have added fea‐
        tures that may not yet be supported by the drivers you use.  Talk to
        the authors of your drivers if you need a new feature that’s not yet
        supported.
 
        Features added after DBI 1.21 (February 2002) are marked in the text
        with the version number of the DBI release they first appeared in.
 
        Extensions to the DBI API often use the "DBIx::*" namespace.  See "Nam‐
        ing Conventions and Name Space". DBI extension modules can be found at
        <http://search.cpan.org/search?mode=module&query=DBIx>.  And all mod‐
        ules related to the DBI can be found at
        <http://search.cpan.org/search?query=DBI&mode=all>.
 

DESCRIPTION

        The DBI is a database access module for the Perl programming language.
        It defines a set of methods, variables, and conventions that provide a
        consistent database interface, independent of the actual database being
        used.
 
        It is important to remember that the DBI is just an interface.  The DBI
        is a layer of "glue" between an application and one or more database
        driver modules.  It is the driver modules which do most of the real
        work. The DBI provides a standard interface and framework for the
        drivers to operate within.
 
        Architecture of a DBI Application
 
                     |<- Scope of DBI ->|
                          .-.   .--------------.   .-------------.
          .-------.       | |---| XYZ Driver   |---| XYZ Engine  |
          | Perl  |       | |   ‘--------------’   ‘-------------’
          | script|  |A|  |D|   .--------------.   .-------------.
          | using |--|P|--|B|---|Oracle Driver |---|Oracle Engine|
          | DBI   |  |I|  |I|   ‘--------------’   ‘-------------’
          | API   |       | |...
          |methods|       | |... Other drivers
          ‘-------’       | |...
                          ‘-’
 
        The API, or Application Programming Interface, defines the call inter‐
        face and variables for Perl scripts to use. The API is implemented by
        the Perl DBI extension.
 
        The DBI "dispatches" the method calls to the appropriate driver for
        actual execution.  The DBI is also responsible for the dynamic loading
        of drivers, error checking and handling, providing default implementa‐
        tions for methods, and many other non-database specific duties.
 
        Each driver contains implementations of the DBI methods using the pri‐
        vate interface functions of the corresponding database engine.  Only
        authors of sophisticated/multi-database applications or generic library
        functions need be concerned with drivers.
 
        Notation and Conventions
 
        The following conventions are used in this document:
 
          $dbh    Database handle object
          $sth    Statement handle object
          $drh    Driver handle object (rarely seen or used in applications)
          $h      Any of the handle types above ($dbh, $sth, or $drh)
          $rc     General Return Code  (boolean: true=ok, false=error)
          $rv     General Return Value (typically an integer)
          @ary    List of values returned from the database, typically a row of data
          $rows   Number of rows processed (if available, else -1)
          $fh     A filehandle
          undef   NULL values are represented by undefined values in Perl
          \%attr  Reference to a hash of attribute values passed to methods
 
        Note that Perl will automatically destroy database and statement handle
        objects if all references to them are deleted.
 
        Outline Usage
 
        To use DBI, first you need to load the DBI module:
 
          use DBI;
          use strict;
 
        (The "use strict;" isn’t required but is strongly recommended.)
 
        Then you need to "connect" to your data source and get a handle for
        that connection:
 
          $dbh = DBI->connect($dsn, $user, $password,
                              { RaiseError => 1, AutoCommit => 0 });
 
        Since connecting can be expensive, you generally just connect at the
        start of your program and disconnect at the end.
 
        Explicitly defining the required "AutoCommit" behaviour is strongly
        recommended and may become mandatory in a later version.  This deter‐
        mines whether changes are automatically committed to the database when
        executed, or need to be explicitly committed later.
 
        The DBI allows an application to "prepare" statements for later execu‐
        tion.  A prepared statement is identified by a statement handle held in
        a Perl variable.  We’ll call the Perl variable $sth in our examples.
 
        The typical method call sequence for a "SELECT" statement is:
 
          prepare,
            execute, fetch, fetch, ...
            execute, fetch, fetch, ...
            execute, fetch, fetch, ...
 
        for example:
 
          $sth = $dbh->prepare("SELECT foo, bar FROM table WHERE baz=?");
 
          $sth->execute( $baz );
 
          while ( @row = $sth->fetchrow_array ) {
            print "@row\n";
          }
 
        The typical method call sequence for a non-"SELECT" statement is:
 
          prepare,
            execute,
            execute,
            execute.
 
        for example:
 
          $sth = $dbh->prepare("INSERT INTO table(foo,bar,baz) VALUES (?,?,?)");
 
          while(<CSV>) {
            chomp;
            my ($foo,$bar,$baz) = split /,/;
                $sth->execute( $foo, $bar, $baz );
          }
 
        The "do()" method can be used for non repeated non-"SELECT" statement
        (or with drivers that don’t support placeholders):
 
          $rows_affected = $dbh->do("UPDATE your_table SET foo = foo + 1");
 
        To commit your changes to the database (when "AutoCommit" is off):
 
          $dbh->commit;  # or call $dbh->rollback; to undo changes
 
        Finally, when you have finished working with the data source, you
        should "disconnect" from it:
 
          $dbh->disconnect;
 
        General Interface Rules & Caveats
 
        The DBI does not have a concept of a "current session". Every session
        has a handle object (i.e., a $dbh) returned from the "connect" method.
        That handle object is used to invoke database related methods.
 
        Most data is returned to the Perl script as strings. (Null values are
        returned as "undef".)  This allows arbitrary precision numeric data to
        be handled without loss of accuracy.  Beware that Perl may not preserve
        the same accuracy when the string is used as a number.
 
        Dates and times are returned as character strings in the current
        default format of the corresponding database engine.  Time zone effects
        are database/driver dependent.
 
        Perl supports binary data in Perl strings, and the DBI will pass binary
        data to and from the driver without change. It is up to the driver
        implementors to decide how they wish to handle such binary data.
 
        Most databases that understand multiple character sets have a default
        global charset. Text stored in the database is, or should be, stored in
        that charset; if not, then that’s the fault of either the database or
        the application that inserted the data. When text is fetched it should
        be automatically converted to the charset of the client, presumably
        based on the locale. If a driver needs to set a flag to get that
        behaviour, then it should do so; it should not require the application
        to do that.
 
        Multiple SQL statements may not be combined in a single statement han‐
        dle ($sth), although some databases and drivers do support this
        (notably Sybase and SQL Server).
 
        Non-sequential record reads are not supported in this version of the
        DBI.  In other words, records can only be fetched in the order that the
        database returned them, and once fetched they are forgotten.
 
        Positioned updates and deletes are not directly supported by the DBI.
        See the description of the "CursorName" attribute for an alternative.
 
        Individual driver implementors are free to provide any private func‐
        tions and/or handle attributes that they feel are useful.  Private
        driver functions can be invoked using the DBI "func()" method.  Private
        driver attributes are accessed just like standard attributes.
 
        Many methods have an optional "\%attr" parameter which can be used to
        pass information to the driver implementing the method. Except where
        specifically documented, the "\%attr" parameter can only be used to
        pass driver specific hints. In general, you can ignore "\%attr" parame‐
        ters or pass it as "undef".
 
        Naming Conventions and Name Space
 
        The DBI package and all packages below it ("DBI::*") are reserved for
        use by the DBI. Extensions and related modules use the "DBIx::" names‐
        pace (see <http://www.perl.com/CPAN/modules/by-module/DBIx/>).  Package
        names beginning with "DBD::" are reserved for use by DBI database
        drivers.  All environment variables used by the DBI or by individual
        DBDs begin with ""DBI_"" or ""DBD_"".
 
        The letter case used for attribute names is significant and plays an
        important part in the portability of DBI scripts.  The case of the
        attribute name is used to signify who defined the meaning of that name
        and its values.
 
          Case of name  Has a meaning defined by
          ------------  ------------------------
          UPPER_CASE    Standards, e.g.,  X/Open, ISO SQL92 etc (portable)
          MixedCase     DBI API (portable), underscores are not used.
          lower_case    Driver or database engine specific (non-portable)
 
        It is of the utmost importance that Driver developers only use lower‐
        case attribute names when defining private attributes. Private
        attribute names must be prefixed with the driver name or suitable
        abbreviation (e.g., ""ora_"" for Oracle, ""ing_"" for Ingres, etc).
 
        SQL - A Query Language
 
        Most DBI drivers require applications to use a dialect of SQL (Struc‐
        tured Query Language) to interact with the database engine.  The "Stan‐
        dards Reference Information" section provides links to useful informa‐
        tion about SQL.
 
        The DBI itself does not mandate or require any particular language to
        be used; it is language independent. In ODBC terms, the DBI is in
        "pass-thru" mode, although individual drivers might not be. The only
        requirement is that queries and other statements must be expressed as a
        single string of characters passed as the first argument to the "pre‐
        pare" or "do" methods.
 
        For an interesting diversion on the real history of RDBMS and SQL, from
        the people who made it happen, see:
 
http://ftp.digital.com/pub/DEC/SRC/technical-notes/SRC-1997-018-html/sqlr95.html
 
        Follow the "Full Contents" then "Intergalactic dataspeak" links for the
        SQL history.
 
        Placeholders and Bind Values
 
        Some drivers support placeholders and bind values.  Placeholders, also
        called parameter markers, are used to indicate values in a database
        statement that will be supplied later, before the prepared statement is
        executed.  For example, an application might use the following to
        insert a row of data into the SALES table:
 
          INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)
 
        or the following, to select the description for a product:
 
          SELECT description FROM products WHERE product_code = ?
 
        The "?" characters are the placeholders.  The association of actual
        values with placeholders is known as binding, and the values are
        referred to as bind values.
 
        Note that the "?" is not enclosed in quotation marks, even when the
        placeholder represents a string.  Some drivers also allow placeholders
        like ":"name and ":"n (e.g., ":1", ":2", and so on) in addition to "?",
        but their use is not portable.
 
        With most drivers, placeholders can’t be used for any element of a
        statement that would prevent the database server from validating the
        statement and creating a query execution plan for it. For example:
 
          "SELECT name, age FROM ?"         # wrong (will probably fail)
          "SELECT name, ?   FROM people"    # wrong (but may not ’fail’)
 
        Also, placeholders can only represent single scalar values.  For exam‐
        ple, the following statement won’t work as expected for more than one
        value:
 
          "SELECT name, age FROM people WHERE name IN (?)"    # wrong
          "SELECT name, age FROM people WHERE name IN (?,?)"  # two names
 
        When using placeholders with the SQL "LIKE" qualifier, you must remem‐
        ber that the placeholder substitutes for the whole string.  So you
        should use ""... LIKE ? ..."" and include any wildcard characters in
        the value that you bind to the placeholder.
 
        NULL Values
 
        Undefined values, or "undef", are used to indicate NULL values.  You
        can insert and update columns with a NULL value as you would a non-NULL
        value.  These examples insert and update the column "age" with a NULL
        value:
 
          $sth = $dbh->prepare(qq{
            INSERT INTO people (fullname, age) VALUES (?, ?)
          });
          $sth->execute("Joe Bloggs", undef);
 
          $sth = $dbh->prepare(qq{
            UPDATE people SET age = ? WHERE fullname = ?
          });
          $sth->execute(undef, "Joe Bloggs");
 
        However, care must be taken when trying to use NULL values in a "WHERE"
        clause.  Consider:
 
          SELECT fullname FROM people WHERE age = ?
 
        Binding an "undef" (NULL) to the placeholder will not select rows which
        have a NULL "age"!  At least for database engines that conform to the
        SQL standard.  Refer to the SQL manual for your database engine or any
        SQL book for the reasons for this.  To explicitly select NULLs you have
        to say ""WHERE age IS NULL"".
 
        A common issue is to have a code fragment handle a value that could be
        either "defined" or "undef" (non-NULL or NULL) at runtime.  A simple
        technique is to prepare the appropriate statement as needed, and sub‐
        stitute the placeholder for non-NULL cases:
 
          $sql_clause = defined $age? "age = ?" : "age IS NULL";
          $sth = $dbh->prepare(qq{
            SELECT fullname FROM people WHERE $sql_clause
          });
          $sth->execute(defined $age ? $age : ());
 
        The following technique illustrates qualifying a "WHERE" clause with
        several columns, whose associated values ("defined" or "undef") are in
        a hash %h:
 
          for my $col ("age", "phone", "email") {
            if (defined $h{$col}) {
              push @sql_qual, "$col = ?";
              push @sql_bind, $h{$col};
            }
            else {
              push @sql_qual, "$col IS NULL";
            }
          }
          $sql_clause = join(" AND ", @sql_qual);
          $sth = $dbh->prepare(qq{
              SELECT fullname FROM people WHERE $sql_clause
          });
          $sth->execute(@sql_bind);
 
        The techniques above call prepare for the SQL statement with each call
        to execute.  Because calls to prepare() can be expensive, performance
        can suffer when an application iterates many times over statements like
        the above.
 
        A better solution is a single "WHERE" clause that supports both NULL
        and non-NULL comparisons.  Its SQL statement would need to be prepared
        only once for all cases, thus improving performance.  Several examples
        of "WHERE" clauses that support this are presented below.  But each
        example lacks portability, robustness, or simplicity.  Whether an exam‐
        ple is supported on your database engine depends on what SQL extensions
        it provides, and where it supports the "?"  placeholder in a statement.
 
          0)  age = ?
          1)  NVL(age, xx) = NVL(?, xx)
          2)  ISNULL(age, xx) = ISNULL(?, xx)
          3)  DECODE(age, ?, 1, 0) = 1
          4)  age = ? OR (age IS NULL AND ? IS NULL)
          5)  age = ? OR (age IS NULL AND SP_ISNULL(?) = 1)
          6)  age = ? OR (age IS NULL AND ? = 1)
 
        Statements formed with the above "WHERE" clauses require execute state‐
        ments as follows.  The arguments are required, whether their values are
        "defined" or "undef".
 
          0,1,2,3)  $sth->execute($age);
          4,5)      $sth->execute($age, $age);
          6)        $sth->execute($age, defined($age) ? 0 : 1);
 
        Example 0 should not work (as mentioned earlier), but may work on a few
        database engines anyway (e.g. Sybase).  Example 0 is part of examples
        4, 5, and 6, so if example 0 works, these other examples may work, even
        if the engine does not properly support the right hand side of the "OR"
        expression.
 
        Examples 1 and 2 are not robust: they require that you provide a valid
        column value xx (e.g. ’~’) which is not present in any row.  That means
        you must have some notion of what data won’t be stored in the column,
        and expect clients to adhere to that.
 
        Example 5 requires that you provide a stored procedure (SP_ISNULL in
        this example) that acts as a function: it checks whether a value is
        null, and returns 1 if it is, or 0 if not.
 
        Example 6, the least simple, is probably the most portable, i.e., it
        should work with with most, if not all, database engines.
 
        Here is a table that indicates which examples above are known to work
        on various database engines:
 
                           -----Examples------
                           0  1  2  3  4  5  6
                           -  -  -  -  -  -  -
          Oracle 9         N  Y  N  Y  Y  ?  Y
          Informix IDS 9   N  N  N  Y  N  Y  Y
          MS SQL           N  N  Y  N  Y  ?  Y
          Sybase           Y  N  N  N  N  N  Y
          AnyData,DBM,CSV  Y  N  N  N  Y  Y* Y
 
        * Works only because Example 0 works.
 
        DBI provides a sample perl script that will test the examples above on
        your database engine and tell you which ones work.  It is located in
        the ex/ subdirectory of the DBI source distribution, or here:
        <http://svn.perl.org/modules/dbi/trunk/ex/perl_dbi_nulls_test.pl>
        Please use the script to help us fill-in and maintain this table.
 
        Performance
 
        Without using placeholders, the insert statement shown previously would
        have to contain the literal values to be inserted and would have to be
        re-prepared and re-executed for each row. With placeholders, the insert
        statement only needs to be prepared once. The bind values for each row
        can be given to the "execute" method each time it’s called. By avoiding
        the need to re-prepare the statement for each row, the application typ‐
        ically runs many times faster. Here’s an example:
 
          my $sth = $dbh->prepare(q{
            INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)
          }) or die $dbh->errstr;
          while (<>) {
              chomp;
              my ($product_code, $qty, $price) = split /,/;
              $sth->execute($product_code, $qty, $price) or die $dbh->errstr;
          }
          $dbh->commit or die $dbh->errstr;
 
        See "execute" and "bind_param" for more details.
 
        The "q{...}" style quoting used in this example avoids clashing with
        quotes that may be used in the SQL statement. Use the double-quote like
        "qq{...}" operator if you want to interpolate variables into the
        string.  See "Quote and Quote-like Operators" in perlop for more
        details.
 
        See also the "bind_columns" method, which is used to associate Perl
        variables with the output columns of a "SELECT" statement.
        In this section, we cover the DBI class methods, utility functions, and
        the dynamic attributes associated with generic DBI handles.
 
        DBI Constants
 
        Constants representing the values of the SQL standard types can be
        imported individually by name, or all together by importing the special
        ":sql_types" tag.
 
        The names and values of all the defined SQL standard types can be pro‐
        duced like this:
 
          foreach (@{ $DBI::EXPORT_TAGS{sql_types} }) {
            printf "%s=%d\n", $_, &{"DBI::$_"};
          }
 
        These constants are defined by SQL/CLI, ODBC or both.  "SQL_BIGINT" is
        (currently) omitted, because SQL/CLI and ODBC provide conflicting
        codes.
 
        See the "type_info", "type_info_all", and "bind_param" methods for pos‐
        sible uses.
 
        Note that just because the DBI defines a named constant for a given
        data type doesn’t mean that drivers will support that data type.
 
        DBI Class Methods
 
        The following methods are provided by the DBI class:
 
        "parse_dsn"
              ($scheme, $driver, $attr_string, $attr_hash, $driver_dsn) = DBI->parse_dsn($dsn)
                  or die "Can’t parse DBI DSN ’$dsn’";
 
            Breaks apart a DBI Data Source Name (DSN) and returns the individ‐
            ual parts. If $dsn doesn’t contain a valid DSN then parse_dsn()
            returns an empty list.
 
            $scheme is the first part of the DSN and is currently always ’dbi’.
            $driver is the driver name, possibly defaulted to $ENV{DBI_DRIVER},
            and may be undefined.  $attr_string is the contents of the optional
            attribute string, which may be undefined.  If $attr_string is not
            empty then $attr_hash is a reference to a hash containing the
            parsed attribute names and values.  $driver_dsn is the last part of
            the DBI DSN string. For example:
 
              ($scheme, $driver, $attr_string, $attr_hash, $driver_dsn)
                  = DBI->parse_dsn("DBI:MyDriver(RaiseError=>1):db=test;port=42");
              $scheme      = ’dbi’;
              $driver      = ’MyDriver’;
              $attr_string = ’RaiseError=>1’;
              $attr_hash   = { ’RaiseError’ => ’1’ };
              $driver_dsn  = ’db=test;port=42’;
 
            The parse_dsn() method was added in DBI 1.43.
 
        "connect"
              $dbh = DBI->connect($data_source, $username, $password)
                        or die $DBI::errstr;
              $dbh = DBI->connect($data_source, $username, $password, \%attr)
                        or die $DBI::errstr;
 
            Establishes a database connection, or session, to the requested
            $data_source.  Returns a database handle object if the connection
            succeeds. Use "$dbh->disconnect" to terminate the connection.
 
            If the connect fails (see below), it returns "undef" and sets both
            $DBI::err and $DBI::errstr. (It does not explicitly set $!.) You
            should generally test the return status of "connect" and "print
            $DBI::errstr" if it has failed.
 
            Multiple simultaneous connections to multiple databases through
            multiple drivers can be made via the DBI. Simply make one "connect"
            call for each database and keep a copy of each returned database
            handle.
 
            The $data_source value must begin with ""dbi:"driver_name":"".  The
            driver_name specifies the driver that will be used to make the con‐
            nection. (Letter case is significant.)
 
            As a convenience, if the $data_source parameter is undefined or
            empty, the DBI will substitute the value of the environment vari‐
            able "DBI_DSN".  If just the driver_name part is empty (i.e., the
            $data_source prefix is ""dbi::""), the environment variable
            "DBI_DRIVER" is used. If neither variable is set, then "connect"
            dies.
 
            Examples of $data_source values are:
 
              dbi:DriverName:database_name
              dbi:DriverName:database_name@hostname:port
              dbi:DriverName:database=database_name;host=hostname;port=port
 
            There is no standard for the text following the driver name. Each
            driver is free to use whatever syntax it wants. The only require‐
            ment the DBI makes is that all the information is supplied in a
            single string.  You must consult the documentation for the drivers
            you are using for a description of the syntax they require.
 
            It is recommended that drivers support the ODBC style, shown in the
            last example above. It is also recommended that that they support
            the three common names ’"host"’, ’"port"’, and ’"database"’ (plus
            ’"db"’ as an alias for "database"). This simplifies automatic con‐
            struction of basic DSNs:
            "dbi:$driver:database=$db;host=$host;port=$port".  Drivers should
            aim to ’do something reasonable’ when given a DSN in this form, but
            if any part is meaningless for that driver (such as ’port’ for
            Informix) it should generate an error if that part is not empty.
 
            If the environment variable "DBI_AUTOPROXY" is defined (and the
            driver in $data_source is not ""Proxy"") then the connect request
            will automatically be changed to:
 
              $ENV{DBI_AUTOPROXY};dsn=$data_source
 
            "DBI_AUTOPROXY" is typically set as ""dbi:Proxy:host‐
            name=...;port=..."".  If $ENV{DBI_AUTOPROXY} doesn’t begin with
            ’"dbi:"’ then "dbi:Proxy:" will be prepended to it first.  See the
            DBD::Proxy documentation for more details.
 
            If $username or $password are undefined (rather than just empty),
            then the DBI will substitute the values of the "DBI_USER" and
            "DBI_PASS" environment variables, respectively.  The DBI will warn
            if the environment variables are not defined.  However, the every‐
            day use of these environment variables is not recommended for secu‐
            rity reasons. The mechanism is primarily intended to simplify test‐
            ing.  See below for alternative way to specify the username and
            password.
 
            "DBI->connect" automatically installs the driver if it has not been
            installed yet. Driver installation either returns a valid driver
            handle, or it dies with an error message that includes the string
            ""install_driver"" and the underlying problem. So "DBI->connect"
            will die on a driver installation failure and will only return
            "undef" on a connect failure, in which case $DBI::errstr will hold
            the error message.  Use "eval { ... }" if you need to catch the
            ""install_driver"" error.
 
            The $data_source argument (with the ""dbi:...:"" prefix removed)
            and the $username and $password arguments are then passed to the
            driver for processing. The DBI does not define any interpretation
            for the contents of these fields.  The driver is free to interpret
            the $data_source, $username, and $password fields in any way, and
            supply whatever defaults are appropriate for the engine being
            accessed.  (Oracle, for example, uses the ORACLE_SID and TWO_TASK
            environment variables if no $data_source is specified.)
 
            The "AutoCommit" and "PrintError" attributes for each connection
            default to "on". (See "AutoCommit" and "PrintError" for more infor‐
            mation.)  However, it is strongly recommended that you explicitly
            define "AutoCommit" rather than rely on the default. The "Print‐
            Warn" attribute defaults to on if $^W is true, i.e., perl is run‐
            ning with warnings enabled.
 
            The "\%attr" parameter can be used to alter the default settings of
            "PrintError", "RaiseError", "AutoCommit", and other attributes. For
            example:
 
              $dbh = DBI->connect($data_source, $user, $pass, {
                    PrintError => 0,
                    AutoCommit => 0
              });
 
            The username and password can also be specified using the
            attributes "Username" and "Password", in which case they take
            precedence over the $username and $password parameters.
 
            You can also define connection attribute values within the
            $data_source parameter. For example:
 
              dbi:DriverName(PrintWarn=>1,PrintError=>0,Taint=>1):...
 
            Individual attributes values specified in this way take precedence
            over any conflicting values specified via the "\%attr" parameter to
            "connect".
 
            The "dbi_connect_method" attribute can be used to specify which
            driver method should be called to establish the connection. The
            only useful values are ’connect’, ’connect_cached’, or some spe‐
            cialized case like ’Apache::DBI::connect’ (which is automatically
            the default when running within Apache).
 
            Where possible, each session ($dbh) is independent from the trans‐
            actions in other sessions. This is useful when you need to hold
            cursors open across transactions--for example, if you use one ses‐
            sion for your long lifespan cursors (typically read-only) and
            another for your short update transactions.
 
            For compatibility with old DBI scripts, the driver can be specified
            by passing its name as the fourth argument to "connect" (instead of
            "\%attr"):
 
              $dbh = DBI->connect($data_source, $user, $pass, $driver);
 
            In this "old-style" form of "connect", the $data_source should not
            start with ""dbi:driver_name:"". (If it does, the embedded
            driver_name will be ignored). Also note that in this older form of
            "connect", the "$dbh->{AutoCommit}" attribute is undefined, the
            "$dbh->{PrintError}" attribute is off, and the old "DBI_DBNAME"
            environment variable is checked if "DBI_DSN" is not defined. Beware
            that this "old-style" "connect" will soon be withdrawn in a future
            version of DBI.
 
        "connect_cached"
              $dbh = DBI->connect_cached($data_source, $username, $password)
                        or die $DBI::errstr;
              $dbh = DBI->connect_cached($data_source, $username, $password, \%attr)
                        or die $DBI::errstr;
 
            "connect_cached" is like "connect", except that the database handle
            returned is also stored in a hash associated with the given parame‐
            ters. If another call is made to "connect_cached" with the same
            parameter values, then the corresponding cached $dbh will be
            returned if it is still valid.  The cached database handle is
            replaced with a new connection if it has been disconnected or if
            the "ping" method fails.
 
            That the behaviour of this method differs in several respects from
            the behaviour of persistent connections implemented by Apache::DBI.
            However, if Apache::DBI is loaded then "connect_cached" will use
            it.
 
            Caching connections can be useful in some applications, but it can
            also cause problems, such as too many connections, and so should be
            used with care. In particular, avoid changing the attributes of a
            database handle created via connect_cached() because it will affect
            other code that may be using the same handle.
 
            Where multiple separate parts of a program are using con‐
            nect_cached() to connect to the same database with the same (ini‐
            tial) attributes it is a good idea to add a private attribute to
            the connect_cached() call to effectively limit the scope of the
            caching. For example:
 
              DBI->connect_cached(..., { private_foo_cachekey => "Bar", ... });
 
            Handles returned from that connect_cached() call will only be
            returned by other connect_cached() call elsewhere in the code if
            those other calls also pass in the same attribute values, including
            the private one.  (I’ve used "private_foo_cachekey" here as an
            example, you can use any attribute name with a "private_" prefix.)
 
            Taking that one step further, you can limit a particular con‐
            nect_cached() call to return handles unique to that one place in
            the code by setting the private attribute to a unique value for
            that place:
 
              DBI->connect_cached(..., { private_foo_cachekey => __FILE__.__LINE__, ... });
 
            By using a private attribute you still get connection caching for
            the individual calls to connect_cached() but, by making separate
            database conections for separate parts of the code, the database
            handles are isolated from any attribute changes made to other han‐
            dles.
 
            The cache can be accessed (and cleared) via the "CachedKids"
            attribute:
 
              my $CachedKids_hashref = $dbh->{Driver}->{CachedKids};
              %$CachedKids_hashref = () if $CachedKids_hashref;
 
        "available_drivers"
              @ary = DBI->available_drivers;
              @ary = DBI->available_drivers($quiet);
 
            Returns a list of all available drivers by searching for "DBD::*"
            modules through the directories in @INC. By default, a warning is
            given if some drivers are hidden by others of the same name in ear‐
            lier directories. Passing a true value for $quiet will inhibit the
            warning.
 
        "installed_drivers"
              %drivers = DBI->installed_drivers();
 
            Returns a list of driver name and driver handle pairs for all
            drivers ’installed’ (loaded) into the current process.  The driver
            name does not include the ’DBD::’ prefix.
 
            To get a list of all drivers available in your perl instalation you
            can use "available_drivers".
 
            Added in DBI 1.49.
 
        "installed_versions"
              DBI->installed_versions;
              @ary  = DBI->installed_versions;
              %hash = DBI->installed_versions;
 
            Calls available_drivers() and attempts to load each of them in turn
            using install_driver().  For each load that succeeds the driver
            name and version number are added to a hash. When running under
            DBI::PurePerl drivers which appear not be pure-perl are ignored.
 
            When called in array context the list of successfully loaded
            drivers is returned (without the ’DBD::’ prefix).
 
            When called in scalar context a reference to the hash is returned
            and the hash will also contain other entries for the "DBI" version,
            "OS" name, etc.
 
            When called in a void context the installed_versions() method will
            print out a formatted list of the hash contents, one per line.
 
            Due to the potentially high memory cost and unknown risks of load‐
            ing in an unknown number of drivers that just happen to be
            installed on the system, this method is nor recommended for general
            use.  Use available_drivers() instead.
 
            The installed_versions() method is primarily intended as a quick
            way to see from the command line what’s installed. For example:
 
              perl -MDBI -e ’DBI->installed_versions’
 
            The installed_versions() method was added in DBI 1.38.
 
        "data_sources"
              @ary = DBI->data_sources($driver);
              @ary = DBI->data_sources($driver, \%attr);
 
            Returns a list of data sources (databases) available via the named
            driver.  If $driver is empty or "undef", then the value of the
            "DBI_DRIVER" environment variable is used.
 
            The driver will be loaded if it hasn’t been already. Note that if
            the driver loading fails then data_sources() dies with an error
            message that includes the string ""install_driver"" and the under‐
            lying problem.
 
            Data sources are returned in a form suitable for passing to the
            "connect" method (that is, they will include the ""dbi:$driver:""
            prefix).
 
            Note that many drivers have no way of knowing what data sources
            might be available for it. These drivers return an empty or incom‐
            plete list or may require driver-specific attributes.
 
            There is also a data_sources() method defined for database handles.
 
        "trace"
              DBI->trace($trace_setting)
              DBI->trace($trace_setting, $trace_filename)
              $trace_setting = DBI->trace;
 
            The "DBI->trace" method sets the global default trace settings and
            returns the previous trace settings. It can also be used to change
            where the trace output is sent.
 
            There’s a similar method, "$h->trace", which sets the trace set‐
            tings for the specific handle it’s called on.
 
            See the "TRACING" section for full details about the DBI’s powerful
            tracing facilities.
 
        DBI Utility Functions
 
        In addition to the DBI methods listed in the previous section, the DBI
        package also provides several utility functions.
 
        These can be imported into your code by listing them in the "use"
        statement. For example:
 
          use DBI qw(neat data_diff);
 
        Alternatively, all these utility functions (except hash) can be
        imported using the ":utils" import tag. For example:
 
          use DBI qw(:utils);
 
        "data_string_desc"
              $description = data_string_desc($string);
 
            Returns an informal description of the string. For example:
 
              UTF8 off, ASCII, 42 characters 42 bytes
              UTF8 off, non-ASCII, 42 characters 42 bytes
              UTF8 on, non-ASCII, 4 characters 6 bytes
              UTF8 on but INVALID encoding, non-ASCII, 4 characters 6 bytes
              UTF8 off, undef
 
            The initial "UTF8" on/off refers to Perl’s internal SvUTF8 flag.
            If $string has the SvUTF8 flag set but the sequence of bytes it
            contains are not a valid UTF-8 encoding then data_string_desc()
            will report "UTF8 on but INVALID encoding".
 
            The "ASCII" vs "non-ASCII" portion shows "ASCII" if all the charac‐
            ters in the string are ASCII (have code points <= 127).
 
            The data_string_desc() function was added in DBI 1.46.
 
        "data_string_diff"
              $diff = data_string_diff($a, $b);
 
            Returns an informal description of the first character difference
            between the strings. If both $a and $b contain the same sequence of
            characters then data_string_diff() returns an empty string.  For
            example:
 
             Params a & b     Result
             ------------     ------
             ’aaa’, ’aaa’     ’’
             ’aaa’, ’abc’     ’Strings differ at index 2: a[2]=a, b[2]=b’
             ’aaa’, undef     ’String b is undef, string a has 3 characters’
             ’aaa’, ’aa’      ’String b truncated after 2 characters’
 
            Unicode characters are reported in "\x{XXXX}" format. Unicode code
            points in the range U+0800 to U+08FF are unassigned and most likely
            to occur due to double-encoding. Characters in this range are
            reported as "\x{08XX}=’C’" where "C" is the corresponding latin-1
            character.
 
            The data_string_diff() function only considers logical characters
            and not the underlying encoding. See "data_diff" for an alterna‐
            tive.
 
            The data_string_diff() function was added in DBI 1.46.
 
        "data_diff"
              $diff = data_diff($a, $b);
              $diff = data_diff($a, $b, $logical);
 
            Returns an informal description of the difference between two
            strings.  It calls "data_string_desc" and "data_string_diff" and
            returns the combined results as a multi-line string.
 
            For example, "data_diff("abc", "ab\x{263a}")" will return:
 
              a: UTF8 off, ASCII, 3 characters 3 bytes
              b: UTF8 on, non-ASCII, 3 characters 5 bytes
              Strings differ at index 2: a[2]=c, b[2]=\x{263A}
 
            If $a and $b are identical in both the characters they contain and
            their physical encoding then data_diff() returns an empty string.
            If $logical is true then physical encoding differences are ignored
            (but are still reported if there is a difference in the charac‐
            ters).
 
            The data_diff() function was added in DBI 1.46.
 
        "neat"
              $str = neat($value);
              $str = neat($value, $maxlen);
 
            Return a string containing a neat (and tidy) representation of the
            supplied value.
 
            Strings will be quoted, although internal quotes will not be
            escaped.  Values known to be numeric will be unquoted. Undefined
            (NULL) values will be shown as "undef" (without quotes).
 
            If the string is flagged internally as utf8 then double quotes will
            be used, otherwise single quotes are used and unprintable charac‐
            ters will be replaced by dot (.).
 
            For result strings longer than $maxlen the result string will be
            truncated to "$maxlen-4" and ""...’"" will be appended.  If $maxlen
            is 0 or "undef", it defaults to $DBI::neat_maxlen which, in turn,
            defaults to 400.
 
            This function is designed to format values for human consumption.
            It is used internally by the DBI for "trace" output. It should typ‐
            ically not be used for formatting values for database use.  (See
            also "quote".)
 
        "neat_list"
              $str = neat_list(\@listref, $maxlen, $field_sep);
 
            Calls "neat" on each element of the list and returns a string con‐
            taining the results joined with $field_sep. $field_sep defaults to
            ", ".
 
        "looks_like_number"
              @bool = looks_like_number(@array);
 
            Returns true for each element that looks like a number.  Returns
            false for each element that does not look like a number.  Returns
            "undef" for each element that is undefined or empty.
 
        "hash"
              $hash_value = DBI::hash($buffer, $type);
 
            Return a 32-bit integer ’hash’ value corresponding to the contents
            of $buffer.  The $type parameter selects which kind of hash algo‐
            rithm should be used.
 
            For the technically curious, type 0 (which is the default if $type
            isn’t specified) is based on the Perl 5.1 hash except that the
            value is forced to be negative (for obscure historical reasons).
            Type 1 is the better "Fowler / Noll / Vo" (FNV) hash. See
            <http://www.isthe.com/chongo/tech/comp/fnv/> for more information.
            Both types are implemented in C and are very fast.
 
            This function doesn’t have much to do with databases, except that
            it can be handy to store hash values in a database.
 
        DBI Dynamic Attributes
 
        Dynamic attributes are always associated with the last handle used
        (that handle is represented by $h in the descriptions below).
 
        Where an attribute is equivalent to a method call, then refer to the
        method call for all related documentation.
 
        Warning: these attributes are provided as a convenience but they do
        have limitations. Specifically, they have a short lifespan: because
        they are associated with the last handle used, they should only be used
        immediately after calling the method that "sets" them.  If in any
        doubt, use the corresponding method call.
 
        $DBI::err
            Equivalent to "$h->err".
 
        $DBI::errstr
            Equivalent to "$h->errstr".
 
        $DBI::state
            Equivalent to "$h->state".
 
        $DBI::rows
            Equivalent to "$h->rows". Please refer to the documentation for the
            "rows" method.
 
        $DBI::lasth
            Returns the DBI object handle used for the most recent DBI method
            call.  If the last DBI method call was a DESTROY then $DBI::lasth
            will return the handle of the parent of the destroyed handle, if
            there is one.
        The following methods can be used by all types of DBI handles.
 
        "err"
              $rv = $h->err;
 
            Returns the native database engine error code from the last driver
            method called. The code is typically an integer but you should not
            assume that.
 
            The DBI resets $h->err to undef before almost all DBI method calls,
            so the value only has a short lifespan. Also, for most drivers, the
            statement handles share the same error variable as the parent
            database handle, so calling a method on one handle may reset the
            error on the related handles.
 
            (Methods which don’t reset err before being called include err()
            and errstr(), obviously, state(), rows(), func(), trace(),
            trace_msg(), ping(), and the tied hash attribute FETCH() and
            STORE() methods.)
 
            If you need to test for specific error conditions and have your
            program be portable to different database engines, then you’ll need
            to determine what the corresponding error codes are for all those
            engines and test for all of them.
 
            A driver may return 0 from err() to indicate a warning condition
            after a method call. Similarly, a driver may return an empty string
            to indicate a ’success with information’ condition. In both these
            cases the value is false but not undef. The errstr() and state()
            methods may be used to retrieve extra information in these cases.
 
            See "set_err" for more information.
 
        "errstr"
              $str = $h->errstr;
 
            Returns the native database engine error message from the last DBI
            method called. This has the same lifespan issues as the "err"
            method described above.
 
            The returned string may contain multiple messages separated by
            newline characters.
 
            The errstr() method should not be used to test for errors, use
            err() for that, because drivers may return ’success with informa‐
            tion’ or warning messages via errstr() for methods that have not
            ’failed’.
 
            See "set_err" for more information.
 
        "state"
              $str = $h->state;
 
            Returns a state code in the standard SQLSTATE five character for‐
            mat.  Note that the specific success code 00000 is translated to
            any empty string (false). If the driver does not support SQLSTATE
            (and most don’t), then state will return "S1000" (General Error)
            for all errors.
 
            The driver is free to return any value via "state", e.g., warning
            codes, even if it has not declared an error by returning a true
            value via the "err" method described above.
 
            The state() method should not be used to test for errors, use err()
            for that, because drivers may return a ’success with information’
            or warning state code via errstr() for methods that have not
            ’failed’.
 
        "set_err"
              $rv = $h->set_err($err, $errstr);
              $rv = $h->set_err($err, $errstr, $state);
              $rv = $h->set_err($err, $errstr, $state, $method);
              $rv = $h->set_err($err, $errstr, $state, $method, $rv);
 
            Set the "err", "errstr", and "state" values for the handle.  This
            method is typically only used by DBI drivers and DBI subclasses.
 
            If the "HandleSetErr" attribute holds a reference to a subroutine
            it is called first. The subroutine can alter the $err, $errstr,
            $state, and $method values. See "HandleSetErr" for full details.
            If the subroutine returns a true value then the handle "err",
            "errstr", and "state" values are not altered and set_err() returns
            an empty list (it normally returns $rv which defaults to undef, see
            below).
 
            Setting "err" to a true value indicates an error and will trigger
            the normal DBI error handling mechanisms, such as "RaiseError" and
            "HandleError", if they are enabled, when execution returns from the
            DBI back to the application.
 
            Setting "err" to "" indicates an ’information’ state, and setting
            it to "0" indicates a ’warning’ state. Setting "err" to "undef"
            also sets "errstr" to undef, and "state" to "", irrespective of the
            values of the $errstr and $state parameters.
 
            The $method parameter provides an alternate method name for the
            "RaiseError"/"PrintError"/"PrintWarn" error string instead of the
            fairly unhelpful ’"set_err"’.
 
            The "set_err" method normally returns undef.  The $rv parameter
            provides an alternate return value.
 
            Some special rules apply if the "err" or "errstr" values for the
            handle are already set...
 
            If "errstr" is true then: "" [err was %s now %s]"" is appended if
            $err is true and "err" is already true; "" [state was %s now %s]""
            is appended if $state is true and "state" is already true; then
            ""\n"" and the new $errstr are appended. Obviously the %s’s above
            are replaced by the corresponding values.
 
            The handle "err" value is set to $err if: $err is true; or handle
            "err" value is undef; or $err is defined and the length is greater
            than the handle "err" length. The effect is that an ’information’
            state only overrides undef; a ’warning’ overrides undef or ’infor‐
            mation’, and an ’error’ state overrides anything.
 
            The handle "state" value is set to $state if $state is true and the
            handle "err" value was set (by the rules above).
 
            Support for warning and information states was added in DBI 1.41.
 
        "trace"
              $h->trace($trace_settings);
              $h->trace($trace_settings, $trace_filename);
              $trace_settings = $h->trace;
 
            The trace() method is used to alter the trace settings for a handle
            (and any future children of that handle).  It can also be used to
            change where the trace output is sent.
 
            There’s a similar method, "DBI->trace", which sets the global
            default trace settings.
 
            See the "TRACING" section for full details about the DBI’s powerful
            tracing facilities.
 
        "trace_msg"
              $h->trace_msg($message_text);
              $h->trace_msg($message_text, $min_level);
 
            Writes $message_text to the trace file if the trace level is
            greater than or equal to $min_level (which defaults to 1).  Can
            also be called as "DBI->trace_msg($msg)".
 
            See "TRACING" for more details.
 
        "func"
              $h->func(@func_arguments, $func_name) or die ...;
 
            The "func" method can be used to call private non-standard and non-
            portable methods implemented by the driver. Note that the function
            name is given as the last argument.
 
            It’s also important to note that the func() method does not clear a
            previous error ($DBI::err etc.) and it does not trigger automatic
            error detection (RaiseError etc.) so you must check the return sta‐
            tus and/or $h->err to detect errors.
 
            (This method is not directly related to calling stored procedures.
            Calling stored procedures is currently not defined by the DBI.
            Some drivers, such as DBD::Oracle, support it in non-portable ways.
            See driver documentation for more details.)
 
            See also "install_method" for how you can avoid needing to use
            func() and gain.
 
        "can"
              $is_implemented = $h->can($method_name);
 
            Returns true if $method_name is implemented by the driver or a
            default method is provided by the DBI.  It returns false where a
            driver hasn’t implemented a method and the default method is pro‐
            vided by the DBI is just an empty stub.
 
        "parse_trace_flags"
              $trace_settings_integer = $h->parse_trace_flags($trace_settings);
 
            Parses a string containing trace settings and returns the corre‐
            sponding integer value used internally by the DBI and drivers.
 
            The $trace_settings argument is a string containing a trace level
            between 0 and 15 and/or trace flag names separated by vertical bar
            (""|"") or comma ("","") characters. For example: "SQL|3|foo".
 
            It uses the parse_trace_flag() method, described below, to process
            the individual trage flag names.
 
            The parse_trace_flags() method was added in DBI 1.42.
 
        "parse_trace_flag"
              $bit_flag = $h->parse_trace_flag($trace_flag_name);
 
            Returns the bit flag corresponding to the trace flag name in
            $trace_flag_name.  Drivers are expected to override this method and
            check if $trace_flag_name is a driver specific trace flags and, if
            not, then call the DBIs default parse_trace_flag().
 
            The parse_trace_flag() method was added in DBI 1.42.
 
        "swap_inner_handle"
              $rc = $h1->swap_inner_handle( $h2 );
              $rc = $h1->swap_inner_handle( $h2, $allow_reparent );
 
            Brain transplants for handles. You don’t need to know about this
            unless you want to become a handle surgeon.
 
            A DBI handle is a reference to a tied hash. A tied hash has an
            inner hash that actually holds the contents.  The swap_inner_han‐
            dle() method swaps the inner hashes between two handles. The $h1
            and $h2 handles still point to the same tied hashes, but what those
            hashes are tied to has been swapped.  In effect $h1 becomes $h2 and
            vice-versa. This is powerful stuff, expect problems. Use with care.
 
            As a small safety measure, the two handles, $h1 and $h2, have to
            share the same parent unless $allow_reparent is true.
 
            The swap_inner_handle() method was added in DBI 1.44.
 
            Here’s a quick kind of ’diagram’ as a worked example to help think
            about what’s happening:
 
                Original state:
                        dbh1o -> dbh1i
                        sthAo -> sthAi(dbh1i)
                        dbh2o -> dbh2i
 
                swap_inner_handle dbh1o with dbh2o:
                        dbh2o -> dbh1i
                        sthAo -> sthAi(dbh1i)
                        dbh1o -> dbh2i
 
                create new sth from dbh1o:
                        dbh2o -> dbh1i
                        sthAo -> sthAi(dbh1i)
                        dbh1o -> dbh2i
                        sthBo -> sthBi(dbh2i)
 
                swap_inner_handle sthAo with sthBo:
                        dbh2o -> dbh1i
                        sthBo -> sthAi(dbh1i)
                        dbh1o -> dbh2i
                        sthAo -> sthBi(dbh2i)
        These attributes are common to all types of DBI handles.
 
        Some attributes are inherited by child handles. That is, the value of
        an inherited attribute in a newly created statement handle is the same
        as the value in the parent database handle. Changes to attributes in
        the new statement handle do not affect the parent database handle and
        changes to the database handle do not affect existing statement han‐
        dles, only future ones.
 
        Attempting to set or get the value of an unknown attribute generates a
        warning, except for private driver specific attributes (which all have
        names starting with a lowercase letter).
 
        Example:
 
          $h->{AttributeName} = ...;    # set/write
          ... = $h->{AttributeName};    # get/read
 
        "Warn" (boolean, inherited)
            The "Warn" attribute enables useful warnings for certain bad prac‐
            tices. It is enabled by default and should only be disabled in rare
            circumstances.  Since warnings are generated using the Perl "warn"
            function, they can be intercepted using the Perl $SIG{__WARN__}
            hook.
 
            The "Warn" attribute is not related to the "PrintWarn" attribute.
 
        "Active" (boolean, read-only)
            The "Active" attribute is true if the handle object is "active".
            This is rarely used in applications. The exact meaning of active is
            somewhat vague at the moment. For a database handle it typically
            means that the handle is connected to a database ("$dbh->discon‐
            nect" sets "Active" off).  For a statement handle it typically
            means that the handle is a "SELECT" that may have more data to
            fetch. (Fetching all the data or calling "$sth->finish" sets
            "Active" off.)
 
        "Executed" (boolean)
            The "Executed" attribute is true if the handle object has been
            "executed".  Currently only the $dbh do() method and the $sth exe‐
            cute(), execute_array(), and execute_for_fetch() methods set the
            "Executed" attribute.
 
            When it’s set on a handle it is also set on the parent handle at
            the same time. So calling execute() on a $sth also sets the "Exe‐
            cuted" attribute on the parent $dbh.
 
            The "Executed" attribute for a database handle is cleared by the
            commit() and rollback() methods. The "Executed" attribute of a
            statement handle is not cleared by the DBI under any circumstances
            and so acts as a permanent record of whether the statement handle
            was ever used.
 
            The "Executed" attribute was added in DBI 1.41.
 
        "Kids" (integer, read-only)
            For a driver handle, "Kids" is the number of currently existing
            database handles that were created from that driver handle.  For a
            database handle, "Kids" is the number of currently existing state‐
            ment handles that were created from that database handle.  For a
            statement handle, the value is zero.
 
        "ActiveKids" (integer, read-only)
            Like "Kids", but only counting those that are "Active" (as above).
 
        "CachedKids" (hash ref)
            For a database handle, "CachedKids" returns a reference to the
            cache (hash) of statement handles created by the "prepare_cached"
            method.  For a driver handle, returns a reference to the cache
            (hash) of database handles created by the "connect_cached" method.
 
        "Type" (scalar)
            The "Type" attribute identifies the type of a DBI handle.  Returns
            "dr" for driver handles, "db" for database handles and "st" for
            statement handles.
 
        "ChildHandles" (array ref)
            The ChildHandles attribute contains a reference to an array of all
            the handles created by this handle which are still accessible.  The
            contents of the array are weak-refs and will become undef when the
            handle goes out of scope.
 
            "ChildHandles" returns undef if your perl version does not support
            weak references (check the Scalar::Util module).  The referenced
            array returned should be treated as read-only.
 
            For example, to enumerate all driver handles, database handles and
            statement handles:
 
                sub show_child_handles {
                    my ($h, $level) = @_;
                    $level ||= 0;
                    printf "%sh %s %s\n", $h->{Type}, "\t" x $level, $h;
                    show_child_handles($_, $level + 1)
                        for (grep { defined } @{$h->{ChildHandles}});
                }
 
                my %drivers = DBI->installed_drivers();
                show_child_handles($_) for (values %drivers);
 
        "CompatMode" (boolean, inherited)
            The "CompatMode" attribute is used by emulation layers (such as
            Oraperl) to enable compatible behaviour in the underlying driver
            (e.g., DBD::Oracle) for this handle. Not normally set by applica‐
            tion code.
 
            It also has the effect of disabling the ’quick FETCH’ of attribute
            values from the handles attribute cache. So all attribute values
            are handled by the drivers own FETCH method. This makes them
            slightly slower but is useful for special-purpose drivers like
            DBD::Multiplex.
 
        "InactiveDestroy" (boolean)
            The default value, false, means a handle will be fully destroyed as
            normal when the last reference to it is removed, just as you’d
            expect.
 
            If set true then the handle will be treated by the DESTROY as if it
            was no longer Active, and so the database engine related effects of
            DESTROYing a handle will be skipped.
 
            Think of the name as meaning ’treat the handle as not-Active in the
            DESTROY method’.
 
            For a database handle, this attribute does not disable an explicit
            call to the disconnect method, only the implicit call from DESTROY
            that happens if the handle is still marked as "Active".
 
            This attribute is specifically designed for use in Unix applica‐
            tions that "fork" child processes. Either the parent or the child
            process, but not both, should set "InactiveDestroy" true on all
            their shared handles.  (Note that some databases, including Oracle,
            don’t support passing a database connection across a fork.)
 
            To help tracing applications using fork the process id is shown in
            the trace log whenever a DBI or handle trace() method is called.
            The process id also shown for every method call if the DBI trace
            level (not handle trace level) is set high enough to show the trace
            from the DBI’s method dispatcher, e.g. >= 9.
 
        "PrintWarn" (boolean, inherited)
            The "PrintWarn" attribute controls the printing of warnings
            recorded by the driver.  When set to a true value the DBI will
            check method calls to see if a warning condition has been set. If
            so, the DBI will effectively do a "warn("$class $method warning:
            $DBI::errstr")" where $class is the driver class and $method is the
            name of the method which failed. E.g.,
 
              DBD::Oracle::db execute warning: ... warning text here ...
 
            By default, "DBI->connect" sets "PrintWarn" "on" if $^W is true,
            i.e., perl is running with warnings enabled.
 
            If desired, the warnings can be caught and processed using a
            $SIG{__WARN__} handler or modules like CGI::Carp and CGI::Error‐
            Wrap.
 
            See also "set_err" for how warnings are recorded and "HandleSetErr"
            for how to influence it.
 
            Fetching the full details of warnings can require an extra round-
            trip to the database server for some drivers. In which case the
            driver may opt to only fetch the full details of warnings if the
            "PrintWarn" attribute is true. If "PrintWarn" is false then these
            drivers should still indicate the fact that there were warnings by
            setting the warning string to, for example: "3 warnings".
 
        "PrintError" (boolean, inherited)
            The "PrintError" attribute can be used to force errors to generate
            warnings (using "warn") in addition to returning error codes in the
            normal way.  When set "on", any method which results in an error
            occuring will cause the DBI to effectively do a "warn("$class
            $method failed: $DBI::errstr")" where $class is the driver class
            and $method is the name of the method which failed. E.g.,
 
              DBD::Oracle::db prepare failed: ... error text here ...
 
            By default, "DBI->connect" sets "PrintError" "on".
 
            If desired, the warnings can be caught and processed using a
            $SIG{__WARN__} handler or modules like CGI::Carp and CGI::Error‐
            Wrap.
 
        "RaiseError" (boolean, inherited)
            The "RaiseError" attribute can be used to force errors to raise
            exceptions rather than simply return error codes in the normal way.
            It is "off" by default.  When set "on", any method which results in
            an error will cause the DBI to effectively do a "die("$class
            $method failed: $DBI::errstr")", where $class is the driver class
            and $method is the name of the method that failed. E.g.,
 
              DBD::Oracle::db prepare failed: ... error text here ...
 
            If you turn "RaiseError" on then you’d normally turn "PrintError"
            off.  If "PrintError" is also on, then the "PrintError" is done
            first (naturally).
 
            Typically "RaiseError" is used in conjunction with "eval { ... }"
            to catch the exception that’s been thrown and followed by an "if
            ($@) { ... }" block to handle the caught exception.  For example:
 
              eval {
                ...
                $sth->execute();
                ...
              };
              if ($@) {
                # $sth->err and $DBI::err will be true if error was from DBI
                warn $@; # print the error
                ... # do whatever you need to deal with the error
              }
 
            In that eval block the $DBI::lasth variable can be useful for diag‐
            nosis and reporting if you can’t be sure which handle triggered the
            error.  For example, $DBI::lasth->{Type} and $DBI::lasth->{State‐
            ment}.
 
            See also "Transactions".
 
            If you want to temporarily turn "RaiseError" off (inside a library
            function that is likely to fail, for example), the recommended way
            is like this:
 
              {
                local $h->{RaiseError};  # localize and turn off for this block
                ...
              }
 
            The original value will automatically and reliably be restored by
            Perl, regardless of how the block is exited.  The same logic
            applies to other attributes, including "PrintError".
 
        "HandleError" (code ref, inherited)
            The "HandleError" attribute can be used to provide your own alter‐
            native behaviour in case of errors. If set to a reference to a sub‐
            routine then that subroutine is called when an error is detected
            (at the same point that "RaiseError" and "PrintError" are handled).
 
            The subroutine is called with three parameters: the error message
            string that "RaiseError" and "PrintError" would use, the DBI handle
            being used, and the first value being returned by the method that
            failed (typically undef).
 
            If the subroutine returns a false value then the "RaiseError"
            and/or "PrintError" attributes are checked and acted upon as nor‐
            mal.
 
            For example, to "die" with a full stack trace for any error:
 
              use Carp;
              $h->{HandleError} = sub { confess(shift) };
 
            Or to turn errors into exceptions:
 
              use Exception; # or your own favourite exception module
              $h->{HandleError} = sub { Exception->new(’DBI’)->raise($_[0]) };
 
            It is possible to ’stack’ multiple HandleError handlers by using
            closures:
 
              sub your_subroutine {
                my $previous_handler = $h->{HandleError};
                $h->{HandleError} = sub {
                  return 1 if $previous_handler and &$previous_handler(@_);
                  ... your code here ...
                };
              }
 
            Using a "my" inside a subroutine to store the previous
            "HandleError" value is important.  See perlsub and perlref for more
            information about closures.
 
            It is possible for "HandleError" to alter the error message that
            will be used by "RaiseError" and "PrintError" if it returns false.
            It can do that by altering the value of $_[0]. This example appends
            a stack trace to all errors and, unlike the previous example using
            Carp::confess, this will work "PrintError" as well as "RaiseError":
 
              $h->{HandleError} = sub { $_[0]=Carp::longmess($_[0]); 0; };
 
            It is also possible for "HandleError" to hide an error, to a lim‐
            ited degree, by using "set_err" to reset $DBI::err and
            $DBI::errstr, and altering the return value of the failed method.
            For example:
 
              $h->{HandleError} = sub {
                return 0 unless $_[0] =~ /^\S+ fetchrow_arrayref failed:/;
                return 0 unless $_[1]->err == 1234; # the error to ’hide’
                $h->set_err(undef,undef);   # turn off the error
                $_[2] = [ ... ];    # supply alternative return value
                return 1;
              };
 
            This only works for methods which return a single value and is hard
            to make reliable (avoiding infinite loops, for example) and so
            isn’t recommended for general use!  If you find a good use for it
            then please let me know.
 
        "HandleSetErr" (code ref, inherited)
            The "HandleSetErr" attribute can be used to intercept the setting
            of handle "err", "errstr", and "state" values.  If set to a refer‐
            ence to a subroutine then that subroutine is called whenever
            set_err() is called, typically by the driver or a subclass.
 
            The subroutine is called with five arguments, the first five that
            were passed to set_err(): the handle, the "err", "errstr", and
            "state" values being set, and the method name. These can be altered
            by changing the values in the @_ array. The return value affects
            set_err() behaviour, see "set_err" for details.
 
            It is possible to ’stack’ multiple HandleSetErr handlers by using
            closures. See "HandleError" for an example.
 
            The "HandleSetErr" and "HandleError" subroutines differ in subtle
            but significant ways. HandleError is only invoked at the point
            where the DBI is about to return to the application with "err" set
            true.  It’s not invoked by the failure of a method that’s been
            called by another DBI method.  HandleSetErr, on the other hand, is
            called whenever set_err() is called with a defined "err" value,
            even if false.  So it’s not just for errors, despite the name, but
            also warn and info states.  The set_err() method, and thus Handle‐
            SetErr, may be called multiple times within a method and is usually
            invoked from deep within driver code.
 
            In theory a driver can use the return value from HandleSetErr via
            set_err() to decide whether to continue or not. If set_err()
            returns an empty list, indicating that the HandleSetErr code has
            ’handled’ the ’error’, the driver could then continue instead of
            failing (if that’s a reasonable thing to do).  This isn’t excepted
            to be common and any such cases should be clearly marked in the
            driver documentation and discussed on the dbi-dev mailing list.
 
            The "HandleSetErr" attribute was added in DBI 1.41.
 
        "ErrCount" (unsigned integer)
            The "ErrCount" attribute is incremented whenever the set_err()
            method records an error. It isn’t incremented by warnings or
            information states. It is not reset by the DBI at any time.
 
            The "ErrCount" attribute was added in DBI 1.41. Older drivers may
            not have been updated to use set_err() to record errors and so this
            attribute may not be incremented when using them.
 
        "ShowErrorStatement" (boolean, inherited)
            The "ShowErrorStatement" attribute can be used to cause the rele‐
            vant Statement text to be appended to the error messages generated
            by the "RaiseError", "PrintError", and "PrintWarn" attributes.
            Only applies to errors on statement handles plus the prepare(),
            do(), and the various "select*()" database handle methods.  (The
            exact format of the appended text is subject to change.)
 
            If "$h->{ParamValues}" returns a hash reference of parameter
            (placeholder) values then those are formatted and appended to the
            end of the Statement text in the error message.
 
        "TraceLevel" (integer, inherited)
            The "TraceLevel" attribute can be used as an alternative to the
            "trace" method to set the DBI trace level and trace flags for a
            specific handle.  See "TRACING" for more details.
 
            The "TraceLevel" attribute is especially useful combined with
            "local" to alter the trace settings for just a single block of
            code.
 
        "FetchHashKeyName" (string, inherited)
            The "FetchHashKeyName" attribute is used to specify whether the
            fetchrow_hashref() method should perform case conversion on the
            field names used for the hash keys. For historical reasons it
            defaults to ’"NAME"’ but it is recommended to set it to ’"NAME_lc"’
            (convert to lower case) or ’"NAME_uc"’ (convert to upper case)
            according to your preference.  It can only be set for driver and
            database handles.  For statement handles the value is frozen when
            prepare() is called.
 
        "ChopBlanks" (boolean, inherited)
            The "ChopBlanks" attribute can be used to control the trimming of
            trailing space characters from fixed width character (CHAR) fields.
            No other field types are affected, even where field values have
            trailing spaces.
 
            The default is false (although it is possible that the default may
            change).  Applications that need specific behaviour should set the
            attribute as needed.
 
            Drivers are not required to support this attribute, but any driver
            which does not support it must arrange to return "undef" as the
            attribute value.
 
        "LongReadLen" (unsigned integer, inherited)
            The "LongReadLen" attribute may be used to control the maximum
            length of ’long’ type fields (LONG, BLOB, CLOB, MEMO, etc.) which
            the driver will read from the database automatically when it
            fetches each row of data.
 
            The "LongReadLen" attribute only relates to fetching and reading
            long values; it is not involved in inserting or updating them.
 
            A value of 0 means not to automatically fetch any long data.
            Drivers may return undef or an empty string for long fields when
            "LongReadLen" is 0.
 
            The default is typically 0 (zero) bytes but may vary between
            drivers.  Applications fetching long fields should set this value
            to slightly larger than the longest long field value to be fetched.
 
            Some databases return some long types encoded as pairs of hex dig‐
            its.  For these types, "LongReadLen" relates to the underlying data
            length and not the doubled-up length of the encoded string.
 
            Changing the value of "LongReadLen" for a statement handle after it
            has been "prepare"’d will typically have no effect, so it’s common
            to set "LongReadLen" on the $dbh before calling "prepare".
 
            For most drivers the value used here has a direct effect on the
            memory used by the statement handle while it’s active, so don’t be
            too generous. If you can’t be sure what value to use you could exe‐
            cute an extra select statement to determine the longest value.  For
            example:
 
              $dbh->{LongReadLen} = $dbh->selectrow_array(qq{
                  SELECT MAX(OCTET_LENGTH(long_column_name))
                  FROM table WHERE ...
              });
              $sth = $dbh->prepare(qq{
                  SELECT long_column_name, ... FROM table WHERE ...
              });
 
            You may need to take extra care if the table can be modified
            between the first select and the second being executed. You may
            also need to use a different function if OCTET_LENGTH() does not
            work for long types in your database. For example, for Sybase use
            DATALENGTH() and for Oracle use LENGTHB().
 
            See also "LongTruncOk" for information on truncation of long types.
 
        "LongTruncOk" (boolean, inherited)
            The "LongTruncOk" attribute may be used to control the effect of
            fetching a long field value which has been truncated (typically
            because it’s longer than the value of the "LongReadLen" attribute).
 
            By default, "LongTruncOk" is false and so fetching a long value
            that needs to be truncated will cause the fetch to fail.  (Applica‐
            tions should always be sure to check for errors after a fetch loop
            in case an error, such as a divide by zero or long field trunca‐
            tion, caused the fetch to terminate prematurely.)
 
            If a fetch fails due to a long field truncation when "LongTruncOk"
            is false, many drivers will allow you to continue fetching further
            rows.
 
            See also "LongReadLen".
 
        "TaintIn" (boolean, inherited)
            If the "TaintIn" attribute is set to a true value and Perl is run‐
            ning in taint mode (e.g., started with the "-T" option), then all
            the arguments to most DBI method calls are checked for being
            tainted. This may change.
 
            The attribute defaults to off, even if Perl is in taint mode.  See
            perlsec for more about taint mode.  If Perl is not running in taint
            mode, this attribute has no effect.
 
            When fetching data that you trust you can turn off the TaintIn
            attribute, for that statement handle, for the duration of the fetch
            loop.
 
            The "TaintIn" attribute was added in DBI 1.31.
 
        "TaintOut" (boolean, inherited)
            If the "TaintOut" attribute is set to a true value and Perl is run‐
            ning in taint mode (e.g., started with the "-T" option), then most
            data fetched from the database is considered tainted. This may
            change.
 
            The attribute defaults to off, even if Perl is in taint mode.  See
            perlsec for more about taint mode.  If Perl is not running in taint
            mode, this attribute has no effect.
 
            When fetching data that you trust you can turn off the TaintOut
            attribute, for that statement handle, for the duration of the fetch
            loop.
 
            Currently only fetched data is tainted. It is possible that the
            results of other DBI method calls, and the value of fetched
            attributes, may also be tainted in future versions. That change may
            well break your applications unless you take great care now. If you
            use DBI Taint mode, please report your experience and any sugges‐
            tions for changes.
 
            The "TaintOut" attribute was added in DBI 1.31.
 
        "Taint" (boolean, inherited)
            The "Taint" attribute is a shortcut for "TaintIn" and "TaintOut"
            (it is also present for backwards compatibility).
 
            Setting this attribute sets both "TaintIn" and "TaintOut", and
            retrieving it returns a true value if and only if "TaintIn" and
            "TaintOut" are both set to true values.
 
        "Profile" (inherited)
            The "Profile" attribute enables the collection and reporting of
            method call timing statistics.  See the DBI::Profile module docu‐
            mentation for much more detail.
 
            The "Profile" attribute was added in DBI 1.24.
 
        "private_your_module_name_*"
            The DBI provides a way to store extra information in a DBI handle
            as "private" attributes. The DBI will allow you to store and
            retrieve any attribute which has a name starting with ""private_"".
 
            It is strongly recommended that you use just one private attribute
            (e.g., use a hash ref) and give it a long and unambiguous name that
            includes the module or application name that the attribute relates
            to (e.g., ""private_YourFullModuleName_thingy"").
 
            Because of the way the Perl tie mechanism works you cannot reliably
            use the "||=" operator directly to initialise the attribute, like
            this:
 
              my $foo = $dbh->{private_yourmodname_foo} ||= { ... }; # WRONG
 
            you should use a two step approach like this:
 
              my $foo = $dbh->{private_yourmodname_foo};
              $foo ||= $dbh->{private_yourmodname_foo} = { ... };
 
            This attribute is primarily of interest to people sub-classing DBI.
        This section covers the methods and attributes associated with database
        handles.
 
        Database Handle Methods
 
        The following methods are specified for DBI database handles:
 
        "clone"
              $new_dbh = $dbh->clone();
              $new_dbh = $dbh->clone(\%attr);
 
            The "clone" method duplicates the $dbh connection by connecting
            with the same parameters ($dsn, $user, $password) as originally
            used.
 
            The attributes for the cloned connect are the same as those used
            for the original connect, with some other attribute merged over
            them depending on the \%attr parameter.
 
            If \%attr is given then the attributes it contains are merged into
            the original attributes and override any with the same names.
            Effectively the same as doing:
 
              %attribues_used = ( %original_attributes, %attr );
 
            If \%attr is not given then it defaults to a hash containing all
            the attributes in the attribute cache of $dbh excluding any non-
            code references, plus the main boolean attributes (RaiseError,
            PrintError, AutoCommit, etc.). This behaviour is subject to change.
 
            The clone method can be used even if the database handle is discon‐
            nected.
 
            The "clone" method was added in DBI 1.33. It is very new and likely
            to change.
 
        "data_sources"
              @ary = $dbh->data_sources();
              @ary = $dbh->data_sources(\%attr);
 
            Returns a list of data sources (databases) available via the $dbh
            driver’s data_sources() method, plus any extra data sources that
            the driver can discover via the connected $dbh. Typically the extra
            data sources are other databases managed by the same server process
            that the $dbh is connected to.
 
            Data sources are returned in a form suitable for passing to the
            "connect" method (that is, they will include the ""dbi:$driver:""
            prefix).
 
            The data_sources() method, for a $dbh, was added in DBI 1.38.
 
        "do"
              $rows = $dbh->do($statement)           or die $dbh->errstr;
              $rows = $dbh->do($statement, \%attr)   or die $dbh->errstr;
              $rows = $dbh->do($statement, \%attr, @bind_values) or die ...
 
            Prepare and execute a single statement. Returns the number of rows
            affected or "undef" on error. A return value of "-1" means the num‐
            ber of rows is not known, not applicable, or not available.
 
            This method is typically most useful for non-"SELECT" statements
            that either cannot be prepared in advance (due to a limitation of
            the driver) or do not need to be executed repeatedly. It should not
            be used for "SELECT" statements because it does not return a state‐
            ment handle (so you can’t fetch any data).
 
            The default "do" method is logically similar to:
 
              sub do {
                  my($dbh, $statement, $attr, @bind_values) = @_;
                  my $sth = $dbh->prepare($statement, $attr) or return undef;
                  $sth->execute(@bind_values) or return undef;
                  my $rows = $sth->rows;
                  ($rows == 0) ? "0E0" : $rows; # always return true if no error
              }
 
            For example:
 
              my $rows_deleted = $dbh->do(q{
                  DELETE FROM table
                  WHERE status = ?
              }, undef, ’DONE’) or die $dbh->errstr;
 
            Using placeholders and @bind_values with the "do" method can be
            useful because it avoids the need to correctly quote any variables
            in the $statement. But if you’ll be executing the statement many
            times then it’s more efficient to "prepare" it once and call "exe‐
            cute" many times instead.
 
            The "q{...}" style quoting used in this example avoids clashing
            with quotes that may be used in the SQL statement. Use the double-
            quote-like "qq{...}" operator if you want to interpolate variables
            into the string.  See "Quote and Quote-like Operators" in perlop
            for more details.
 
        "last_insert_id"
              $rv = $dbh->last_insert_id($catalog, $schema, $table, $field);
              $rv = $dbh->last_insert_id($catalog, $schema, $table, $field, \%attr);
 
            Returns a value ’identifying’ the row just inserted, if possible.
            Typically this would be a value assigned by the database server to
            a column with an auto_increment or serial type.  Returns undef if
            the driver does not support the method or can’t determine the
            value.
 
            The $catalog, $schema, $table, and $field parameters may be
            required for some drivers (see below).  If you don’t know the
            parameter values and your driver does not need them, then use
            "undef" for each.
 
            There are several caveats to be aware of with this method if you
            want to use it for portable applications:
 
            * For some drivers the value may only available immediately after
            the insert statement has executed (e.g., mysql, Informix).
 
            * For some drivers the $catalog, $schema, $table, and $field param‐
            eters are required, for others they are ignored (e.g., mysql).
 
            * Drivers may return an indeterminate value if no insert has been
            performed yet.
 
            * For some drivers the value may only be available if placeholders
            have not been used (e.g., Sybase, MS SQL). In this case the value
            returned would be from the last non-placeholder insert statement.
 
            * Some drivers may need driver-specific hints about how to get the
            value. For example, being told the name of the database ’sequence’
            object that holds the value. Any such hints are passed as driver-
            specific attributes in the \%attr parameter.
 
            * If the underlying database offers nothing better, then some
            drivers may attempt to implement this method by executing ""select
            max($field) from $table"". Drivers using any approach like this
            should issue a warning if "AutoCommit" is true because it is gener‐
            ally unsafe - another process may have modified the table between
            your insert and the select. For situations where you know it is
            safe, such as when you have locked the table, you can silence the
            warning by passing "Warn" => 0 in \%attr.
 
            * If no insert has been performed yet, or the last insert failed,
            then the value is implementation defined.
 
            Given all the caveats above, it’s clear that this method must be
            used with care.
 
            The "last_insert_id" method was added in DBI 1.38.
 
        "selectrow_array"
              @row_ary = $dbh->selectrow_array($statement);
              @row_ary = $dbh->selectrow_array($statement, \%attr);
              @row_ary = $dbh->selectrow_array($statement, \%attr, @bind_values);
 
            This utility method combines "prepare", "execute" and
            "fetchrow_array" into a single call. If called in a list context,
            it returns the first row of data from the statement.  The $state‐
            ment parameter can be a previously prepared statement handle, in
            which case the "prepare" is skipped.
 
            If any method fails, and "RaiseError" is not set, "selectrow_array"
            will return an empty list.
 
            If called in a scalar context for a statement handle that has more
            than one column, it is undefined whether the driver will return the
            value of the first column or the last. So don’t do that.  Also, in
            a scalar context, an "undef" is returned if there are no more rows
            or if an error occurred. That "undef" can’t be distinguished from
            an "undef" returned because the first field value was NULL.  For
            these reasons you should exercise some caution if you use "selec‐
            trow_array" in a scalar context, or just don’t do that.
 
        "selectrow_arrayref"
              $ary_ref = $dbh->selectrow_arrayref($statement);
              $ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
              $ary_ref = $dbh->selectrow_arrayref($statement, \%attr, @bind_values);
 
            This utility method combines "prepare", "execute" and
            "fetchrow_arrayref" into a single call. It returns the first row of
            data from the statement.  The $statement parameter can be a previ‐
            ously prepared statement handle, in which case the "prepare" is
            skipped.
 
            If any method fails, and "RaiseError" is not set, "selectrow_array"
            will return undef.
 
        "selectrow_hashref"
              $hash_ref = $dbh->selectrow_hashref($statement);
              $hash_ref = $dbh->selectrow_hashref($statement, \%attr);
              $hash_ref = $dbh->selectrow_hashref($statement, \%attr, @bind_values);
 
            This utility method combines "prepare", "execute" and
            "fetchrow_hashref" into a single call. It returns the first row of
            data from the statement.  The $statement parameter can be a previ‐
            ously prepared statement handle, in which case the "prepare" is
            skipped.
 
            If any method fails, and "RaiseError" is not set, "selec‐
            trow_hashref" will return undef.
 
        "selectall_arrayref"
              $ary_ref = $dbh->selectall_arrayref($statement);
              $ary_ref = $dbh->selectall_arrayref($statement, \%attr);
              $ary_ref = $dbh->selectall_arrayref($statement, \%attr, @bind_values);
 
            This utility method combines "prepare", "execute" and
            "fetchall_arrayref" into a single call. It returns a reference to
            an array containing a reference to an array (or hash, see below)
            for each row of data fetched.
 
            The $statement parameter can be a previously prepared statement
            handle, in which case the "prepare" is skipped. This is recommended
            if the statement is going to be executed many times.
 
            If "RaiseError" is not set and any method except
            "fetchall_arrayref" fails then "selectall_arrayref" will return
            "undef"; if "fetchall_arrayref" fails then it will return with
            whatever data has been fetched thus far. You should check
            "$sth->err" afterwards (or use the "RaiseError" attribute) to dis‐
            cover if the data is complete or was truncated due to an error.
 
            The "fetchall_arrayref" method called by "selectall_arrayref" sup‐
            ports a $max_rows parameter. You can specify a value for $max_rows
            by including a ’"MaxRows"’ attribute in \%attr. In which case fin‐
            ish() is called for you after fetchall_arrayref() returns.
 
            The "fetchall_arrayref" method called by "selectall_arrayref" also
            supports a $slice parameter. You can specify a value for $slice by
            including a ’"Slice"’ or ’"Columns"’ attribute in \%attr. The only
            difference between the two is that if "Slice" is not defined and
            "Columns" is an array ref, then the array is assumed to contain
            column index values (which count from 1), rather than perl array
            index values.  In which case the array is copied and each value
            decremented before passing to "/fetchall_arrayref".
 
            You may often want to fetch an array of rows where each row is
            stored as a hash. That can be done simple using:
 
              my $emps = $dbh->selectall_arrayref(
                  "SELECT ename FROM emp ORDER BY ename",
                  { Slice => {} }
              );
              foreach my $emp ( @$emps ) {
                  print "Employee: $emp->{ename}\n";
              }
 
            Or, to fetch into an array instead of an array ref:
 
              @result = @{ $dbh->selectall_arrayref($sql, { Slice => {} }) };
 
            See "fetchall_arrayref" method for more details.
 
        "selectall_hashref"
              $hash_ref = $dbh->selectall_hashref($statement, $key_field);
              $hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr);
              $hash_ref = $dbh->selectall_hashref($statement, $key_field, \%attr, @bind_values);
 
            This utility method combines "prepare", "execute" and
            "fetchall_hashref" into a single call. It returns a reference to a
            hash containing one entry, at most, for each row, as returned by
            fetchall_hashref().
 
            The $statement parameter can be a previously prepared statement
            handle, in which case the "prepare" is skipped.  This is recom‐
            mended if the statement is going to be executed many times.
 
            The $key_field parameter defines which column, or columns, are used
            as keys in the returned hash. It can either be the name of a single
            field, or a reference to an array containing multiple field names.
            Using multiple names yields a tree of nested hashes.
 
            If a row has the same key as an earlier row then it replaces the
            earlier row.
 
            If any method except "fetchrow_hashref" fails, and "RaiseError" is
            not set, "selectall_hashref" will return "undef".  If
            "fetchrow_hashref" fails and "RaiseError" is not set, then it will
            return with whatever data it has fetched thus far. $DBI::err should
            be checked to catch that.
 
            See fetchall_hashref() for more details.
 
        "selectcol_arrayref"
              $ary_ref = $dbh->selectcol_arrayref($statement);
              $ary_ref = $dbh->selectcol_arrayref($statement, \%attr);
              $ary_ref = $dbh->selectcol_arrayref($statement, \%attr, @bind_values);
 
            This utility method combines "prepare", "execute", and fetching one
            column from all the rows, into a single call. It returns a refer‐
            ence to an array containing the values of the first column from
            each row.
 
            The $statement parameter can be a previously prepared statement
            handle, in which case the "prepare" is skipped. This is recommended
            if the statement is going to be executed many times.
 
            If any method except "fetch" fails, and "RaiseError" is not set,
            "selectcol_arrayref" will return "undef".  If "fetch" fails and
            "RaiseError" is not set, then it will return with whatever data it
            has fetched thus far. $DBI::err should be checked to catch that.
 
            The "selectcol_arrayref" method defaults to pushing a single column
            value (the first) from each row into the result array. However, it
            can also push another column, or even multiple columns per row,
            into the result array. This behaviour can be specified via a
            ’"Columns"’ attribute which must be a ref to an array containing
            the column number or numbers to use. For example:
 
              # get array of id and name pairs:
              my $ary_ref = $dbh->selectcol_arrayref("select id, name from table", { Columns=>[1,2] });
              my %hash = @$ary_ref; # build hash from key-value pairs so $hash{$id} => name
 
            You can specify a maximum number of rows to fetch by including a
            ’"MaxRows"’ attribute in \%attr.
 
        "prepare"
              $sth = $dbh->prepare($statement)          or die $dbh->errstr;
              $sth = $dbh->prepare($statement, \%attr)  or die $dbh->errstr;
 
            Prepares a statement for later execution by the database engine and
            returns a reference to a statement handle object.
 
            The returned statement handle can be used to get attributes of the
            statement and invoke the "execute" method. See "Statement Handle
            Methods".
 
            Drivers for engines without the concept of preparing a statement
            will typically just store the statement in the returned handle and
            process it when "$sth->execute" is called. Such drivers are
            unlikely to give much useful information about the statement, such
            as "$sth->{NUM_OF_FIELDS}", until after "$sth->execute" has been
            called. Portable applications should take this into account.
 
            In general, DBI drivers do not parse the contents of the statement
            (other than simply counting any "Placeholders"). The statement is
            passed directly to the database engine, sometimes known as pass-
            thru mode. This has advantages and disadvantages. On the plus side,
            you can access all the functionality of the engine being used. On
            the downside, you’re limited if you’re using a simple engine, and
            you need to take extra care if writing applications intended to be
            portable between engines.
 
            Portable applications should not assume that a new statement can be
            prepared and/or executed while still fetching results from a previ‐
            ous statement.
 
            Some command-line SQL tools use statement terminators, like a semi‐
            colon, to indicate the end of a statement. Such terminators should
            not normally be used with the DBI.
 
        "prepare_cached"
              $sth = $dbh->prepare_cached($statement)
              $sth = $dbh->prepare_cached($statement, \%attr)
              $sth = $dbh->prepare_cached($statement, \%attr, $if_active)
 
            Like "prepare" except that the statement handle returned will be
            stored in a hash associated with the $dbh. If another call is made
            to "prepare_cached" with the same $statement and %attr parameter
            values, then the corresponding cached $sth will be returned without
            contacting the database server.
 
            The $if_active parameter lets you adjust the behaviour if an
            already cached statement handle is still Active.  There are several
            alternatives:
 
            0: A warning will be generated, and finish() will be called on the
            statement handle before it is returned.  This is the default
            behaviour if $if_active is not passed.
            1: finish() will be called on the statement handle, but the warning
            is suppressed.
            2: Disables any checking.
            3: The existing active statement handle will be removed from the
            cache and a new statement handle prepared and cached in its place.
            This is the safest option because it doesn’t affect the state of
            the old handle, it just removes it from the cache. [Added in DBI
            1.40]
 
            Here are some examples of "prepare_cached":
 
              sub insert_hash {
                my ($table, $field_values) = @_;
                # sort to keep field order, and thus sql, stable for prepare_cached
                my @fields = sort keys %$field_values;
                my @values = @{$field_values}{@fields};
                my $sql = sprintf "insert into %s (%s) values (%s)",
                    $table, join(",", @fields), join(",", ("?")x@fields);
                my $sth = $dbh->prepare_cached($sql);
                return $sth->execute(@values);
              }
 
              sub search_hash {
                my ($table, $field_values) = @_;
                # sort to keep field order, and thus sql, stable for prepare_cached
                my @fields = sort keys %$field_values;
                my @values = @{$field_values}{@fields};
                my $qualifier = "";
                $qualifier = "where ".join(" and ", map { "$_=?" } @fields) if @fields;
                $sth = $dbh->prepare_cached("SELECT * FROM $table $qualifier");
                return $dbh->selectall_arrayref($sth, {}, @values);
              }
 
            Caveat emptor: This caching can be useful in some applications, but
            it can also cause problems and should be used with care. Here is a
            contrived case where caching would cause a significant problem:
 
              my $sth = $dbh->prepare_cached(’SELECT * FROM foo WHERE bar=?’);
              $sth->execute(...);
              while (my $data = $sth->fetchrow_hashref) {
 
                # later, in some other code called within the loop...
                my $sth2 = $dbh->prepare_cached(’SELECT * FROM foo WHERE bar=?’);
                $sth2->execute(...);
                while (my $data2 = $sth2->fetchrow_arrayref) {
                  do_stuff(...);
                }
              }
 
            In this example, since both handles are preparing the exact same
            statement, $sth2 will not be its own statement handle, but a dupli‐
            cate of $sth returned from the cache. The results will certainly
            not be what you expect.  Typically the the inner fetch loop will
            work normally, fetching all the records and terminating when there
            are no more, but now $sth is the same as $sth2 the outer fetch loop
            will also terminate.
 
            You’ll know if you run into this problem because prepare_cached()
            will generate a warning by default (when $if_active is false).
 
            The cache used by prepare_cached() is keyed by both the statement
            and any attributes so you can also avoid this issue by doing some‐
            thing like:
 
              $sth = $dbh->prepare_cached("...", { dbi_dummy => __FILE__.__LINE__ });
 
            which will ensure that prepare_cached only returns statements
            cached by that line of code in that source file.
 
            If you’d like the cache to managed intelligently, you can tie the
            hashref returned by "CachedKids" to an appropriate caching module,
            such as Tie::Cache::LRU:
 
              my $cache = $dbh->{CachedKids};
              tie %$cache, ’Tie::Cache::LRU’, 500;
 
        "commit"
              $rc  = $dbh->commit     or die $dbh->errstr;
 
            Commit (make permanent) the most recent series of database changes
            if the database supports transactions and AutoCommit is off.
 
            If "AutoCommit" is on, then calling "commit" will issue a "commit
            ineffective with AutoCommit" warning.
 
            See also "Transactions" in the "FURTHER INFORMATION" section below.
 
        "rollback"
              $rc  = $dbh->rollback   or die $dbh->errstr;
 
            Rollback (undo) the most recent series of uncommitted database
            changes if the database supports transactions and AutoCommit is
            off.
 
            If "AutoCommit" is on, then calling "rollback" will issue a "roll‐
            back ineffective with AutoCommit" warning.
 
            See also "Transactions" in the "FURTHER INFORMATION" section below.
 
        "begin_work"
              $rc  = $dbh->begin_work   or die $dbh->errstr;
 
            Enable transactions (by turning "AutoCommit" off) until the next
            call to "commit" or "rollback". After the next "commit" or "roll‐
            back", "AutoCommit" will automatically be turned on again.
 
            If "AutoCommit" is already off when "begin_work" is called then it
            does nothing except return an error. If the driver does not support
            transactions then when "begin_work" attempts to set "AutoCommit"
            off the driver will trigger a fatal error.
 
            See also "Transactions" in the "FURTHER INFORMATION" section below.
 
        "disconnect"
              $rc = $dbh->disconnect  or warn $dbh->errstr;
 
            Disconnects the database from the database handle. "disconnect" is
            typically only used before exiting the program. The handle is of
            little use after disconnecting.
 
            The transaction behaviour of the "disconnect" method is, sadly,
            undefined.  Some database systems (such as Oracle and Ingres) will
            automatically commit any outstanding changes, but others (such as
            Informix) will rollback any outstanding changes.  Applications not
            using "AutoCommit" should explicitly call "commit" or "rollback"
            before calling "disconnect".
 
            The database is automatically disconnected by the "DESTROY" method
            if still connected when there are no longer any references to the
            handle.  The "DESTROY" method for each driver should implicitly
            call "rollback" to undo any uncommitted changes. This is vital
            behaviour to ensure that incomplete transactions don’t get commit‐
            ted simply because Perl calls "DESTROY" on every object before
            exiting. Also, do not rely on the order of object destruction dur‐
            ing "global destruction", as it is undefined.
 
            Generally, if you want your changes to be commited or rolled back
            when you disconnect, then you should explicitly call "commit" or
            "rollback" before disconnecting.
 
            If you disconnect from a database while you still have active
            statement handles (e.g., SELECT statement handles that may have
            more data to fetch), you will get a warning. The warning may indi‐
            cate that a fetch loop terminated early, perhaps due to an uncaught
            error.  To avoid the warning call the "finish" method on the active
            handles.
 
        "ping"
              $rc = $dbh->ping;
 
            Attempts to determine, in a reasonably efficient way, if the
            database server is still running and the connection to it is still
            working.  Individual drivers should implement this function in the
            most suitable manner for their database engine.
 
            The current default implementation always returns true without
            actually doing anything. Actually, it returns ""0 but true"" which
            is true but zero. That way you can tell if the return value is gen‐
            uine or just the default. Drivers should override this method with
            one that does the right thing for their type of database.
 
            Few applications would have direct use for this method. See the
            specialized Apache::DBI module for one example usage.
 
        "get_info"
              $value = $dbh->get_info( $info_type );
 
            Returns information about the implementation, i.e. driver and data
            source capabilities, restrictions etc. It returns "undef" for
            unknown or unimplemented information types. For example:
 
              $database_version  = $dbh->get_info(  18 ); # SQL_DBMS_VER
              $max_select_tables = $dbh->get_info( 106 ); # SQL_MAXIMUM_TABLES_IN_SELECT
 
            See "Standards Reference Information" for more detailed information
            about the information types and their meanings and possible return
            values.
 
            The DBI::Const::GetInfoType module exports a %GetInfoType hash that
            can be used to map info type names to numbers. For example:
 
              $database_version = $dbh->get_info( $GetInfoType{SQL_DBMS_VER} );
 
            The names are a merging of the ANSI and ODBC standards (which dif‐
            fer in some cases). See DBI::Const::GetInfoType for more details.
 
            Because some DBI methods make use of get_info(), drivers are
            strongly encouraged to support at least the following very minimal
            set of information types to ensure the DBI itself works properly:
 
             Type  Name                        Example A     Example B
             ----  --------------------------  ------------  ----------------
               17  SQL_DBMS_NAME               ’ACCESS’      ’Oracle’
               18  SQL_DBMS_VER                ’03.50.0000’  ’08.01.0721 ...’
               29  SQL_IDENTIFIER_QUOTE_CHAR   ’‘’           ’"’
               41  SQL_CATALOG_NAME_SEPARATOR  ’.’           ’@’
              114  SQL_CATALOG_LOCATION        1             2
 
        "table_info"
              $sth = $dbh->table_info( $catalog, $schema, $table, $type );
              $sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
 
            Returns an active statement handle that can be used to fetch infor‐
            mation about tables and views that exist in the database.
 
            The arguments $catalog, $schema and $table may accept search pat‐
            terns according to the database/driver, for example: $table =
            ’%FOO%’; Remember that the underscore character (’"_"’) is a search
            pattern that means match any character, so ’FOO_%’ is the same as
            ’FOO%’ and ’FOO_BAR%’ will match names like ’FOO1BAR’.
 
            The value of $type is a comma-separated list of one or more types
            of tables to be returned in the result set. Each value may option‐
            ally be quoted, e.g.:
 
              $type = "TABLE";
              $type = "’TABLE’,’VIEW’";
 
            In addition the following special cases may also be supported by
            some drivers:
 
            * If the value of $catalog is ’%’ and $schema and $table name are
            empty strings, the result set contains a list of catalog names. For
            example:
                  $sth = $dbh->table_info(’%’, ’’, ’’);
 
            * If the value of $schema is ’%’ and $catalog and $table are empty
            strings, the result set contains a list of schema names.
            * If the value of $type is ’%’ and $catalog, $schema, and $table
            are all empty strings, the result set contains a list of table
            types.
 
            If your driver doesn’t support one or more of the selection filter
            parameters then you may get back more than you asked for and can do
            the filtering yourself.
 
            This method can be expensive, and can return a large amount of
            data.  (For example, small Oracle installation returns over 2000
            rows.)  So it’s a good idea to use the filters to limit the data as
            much as possible.
 
            The statement handle returned has at least the following fields in
            the order show below. Other fields, after these, may also be
            present.
 
            TABLE_CAT: Table catalog identifier. This field is NULL ("undef")
            if not applicable to the data source, which is usually the case.
            This field is empty if not applicable to the table.
 
            TABLE_SCHEM: The name of the schema containing the TABLE_NAME
            value.  This field is NULL ("undef") if not applicable to data
            source, and empty if not applicable to the table.
 
            TABLE_NAME: Name of the table (or view, synonym, etc).
 
            TABLE_TYPE: One of the following: "TABLE", "VIEW", "SYSTEM TABLE",
            "GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM" or a type
            identifier that is specific to the data source.
 
            REMARKS: A description of the table. May be NULL ("undef").
 
            Note that "table_info" might not return records for all tables.
            Applications can use any valid table regardless of whether it’s
            returned by "table_info".
 
            See also "tables", "Catalog Methods" and "Standards Reference
            Information".
 
        "column_info"
              $sth = $dbh->column_info( $catalog, $schema, $table, $column );
 
            Returns an active statement handle that can be used to fetch infor‐
            mation about columns in specified tables.
 
            The arguments $schema, $table and $column may accept search pat‐
            terns according to the database/driver, for example: $table =
            ’%FOO%’;
 
            Note: The support for the selection criteria is driver specific. If
            the driver doesn’t support one or more of them then you may get
            back more than you asked for and can do the filtering yourself.
 
            The statement handle returned has at least the following fields in
            the order shown below. Other fields, after these, may also be
            present.
 
            TABLE_CAT: The catalog identifier.  This field is NULL ("undef") if
            not applicable to the data source, which is often the case.  This
            field is empty if not applicable to the table.
 
            TABLE_SCHEM: The schema identifier.  This field is NULL ("undef")
            if not applicable to the data source, and empty if not applicable
            to the table.
 
            TABLE_NAME: The table identifier.  Note: A driver may provide col‐
            umn metadata not only for base tables, but also for derived objects
            like SYNONYMS etc.
 
            COLUMN_NAME: The column identifier.
 
            DATA_TYPE: The concise data type code.
 
            TYPE_NAME: A data source dependent data type name.
 
            COLUMN_SIZE: The column size.  This is the maximum length in char‐
            acters for character data types, the number of digits or bits for
            numeric data types or the length in the representation of temporal
            types.  See the relevant specifications for detailed information.
 
            BUFFER_LENGTH: The length in bytes of transferred data.
 
            DECIMAL_DIGITS: The total number of significant digits to the right
            of the decimal point.
 
            NUM_PREC_RADIX: The radix for numeric precision.  The value is 10
            or 2 for numeric data types and NULL ("undef") if not applicable.
 
            NULLABLE: Indicates if a column can accept NULLs.  The following
            values are defined:
 
              SQL_NO_NULLS          0
              SQL_NULLABLE          1
              SQL_NULLABLE_UNKNOWN  2
 
            REMARKS: A description of the column.
 
            COLUMN_DEF: The default value of the column.
 
            SQL_DATA_TYPE: The SQL data type.
 
            SQL_DATETIME_SUB: The subtype code for datetime and interval data
            types.
 
            CHAR_OCTET_LENGTH: The maximum length in bytes of a character or
            binary data type column.
 
            ORDINAL_POSITION: The column sequence number (starting with 1).
 
            IS_NULLABLE: Indicates if the column can accept NULLs.  Possible
            values are: ’NO’, ’YES’ and ’’.
 
            SQL/CLI defines the following additional columns:
 
              CHAR_SET_CAT
              CHAR_SET_SCHEM
              CHAR_SET_NAME
              COLLATION_CAT
              COLLATION_SCHEM
              COLLATION_NAME
              UDT_CAT
              UDT_SCHEM
              UDT_NAME
              DOMAIN_CAT
              DOMAIN_SCHEM
              DOMAIN_NAME
              SCOPE_CAT
              SCOPE_SCHEM
              SCOPE_NAME
              MAX_CARDINALITY
              DTD_IDENTIFIER
              IS_SELF_REF
 
            Drivers capable of supplying any of those values should do so in
            the corresponding column and supply undef values for the others.
 
            Drivers wishing to provide extra database/driver specific informa‐
            tion should do so in extra columns beyond all those listed above,
            and use lowercase field names with the driver-specific prefix
            (i.e., ’ora_...’). Applications accessing such fields should do so
            by name and not by column number.
 
            The result set is ordered by TABLE_CAT, TABLE_SCHEM, TABLE_NAME and
            ORDINAL_POSITION.
 
            Note: There is some overlap with statement attributes (in perl) and
            SQLDescribeCol (in ODBC). However, SQLColumns provides more meta‐
            data.
 
            See also "Catalog Methods" and "Standards Reference Information".
 
        "primary_key_info"
              $sth = $dbh->primary_key_info( $catalog, $schema, $table );
 
            Returns an active statement handle that can be used to fetch infor‐
            mation about columns that make up the primary key for a table.  The
            arguments don’t accept search patterns (unlike table_info()).
 
            For example:
 
              $sth = $dbh->primary_key_info( undef, $user, ’foo’ );
              $data = $sth->fetchall_arrayref;
 
            The statement handle will return one row per column, ordered by TA‐
            BLE_CAT, TABLE_SCHEM, TABLE_NAME, and KEY_SEQ.  If there is no pri‐
            mary key then the statement handle will fetch no rows.
 
            Note: The support for the selection criteria, such as $catalog, is
            driver specific.  If the driver doesn’t support catalogs and/or
            schemas, it may ignore these criteria.
 
            The statement handle returned has at least the following fields in
            the order shown below. Other fields, after these, may also be
            present.
 
            TABLE_CAT: The catalog identifier.  This field is NULL ("undef") if
            not applicable to the data source, which is often the case.  This
            field is empty if not applicable to the table.
 
            TABLE_SCHEM: The schema identifier.  This field is NULL ("undef")
            if not applicable to the data source, and empty if not applicable
            to the table.
 
            TABLE_NAME: The table identifier.
 
            COLUMN_NAME: The column identifier.
 
            KEY_SEQ: The column sequence number (starting with 1).  Note: This
            field is named ORDINAL_POSITION in SQL/CLI.
 
            PK_NAME: The primary key constraint identifier.  This field is NULL
            ("undef") if not applicable to the data source.
 
            See also "Catalog Methods" and "Standards Reference Information".
 
        "primary_key"
              @key_column_names = $dbh->primary_key( $catalog, $schema, $table );
 
            Simple interface to the primary_key_info() method. Returns a list
            of the column names that comprise the primary key of the specified
            table.  The list is in primary key column sequence order.  If there
            is no primary key then an empty list is returned.
 
        "foreign_key_info"
              $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
                                           , $fk_catalog, $fk_schema, $fk_table );
 
              $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
                                           , $fk_catalog, $fk_schema, $fk_table
                                           , \%attr );
 
            Returns an active statement handle that can be used to fetch infor‐
            mation about foreign keys in and/or referencing the specified ta‐
            ble(s).  The arguments don’t accept search patterns (unlike ta‐
            ble_info()).
 
            $pk_catalog, $pk_schema, $pk_table identify the primary (unique)
            key table (PKT).
 
            $fk_catalog, $fk_schema, $fk_table identify the foreign key table
            (FKT).
 
            If both PKT and FKT are given, the function returns the foreign
            key, if any, in table FKT that refers to the primary (unique) key
            of table PKT.  (Note: In SQL/CLI, the result is implementa‐
            tion-defined.)
 
            If only PKT is given, then the result set contains the primary key
            of that table and all foreign keys that refer to it.
 
            If only FKT is given, then the result set contains all foreign keys
            in that table and the primary keys to which they refer.  (Note: In
            SQL/CLI, the result includes unique keys too.)
 
            For example:
 
              $sth = $dbh->foreign_key_info( undef, $user, ’master’);
              $sth = $dbh->foreign_key_info( undef, undef,   undef , undef, $user, ’detail’);
              $sth = $dbh->foreign_key_info( undef, $user, ’master’, undef, $user, ’detail’);
 
            Note: The support for the selection criteria, such as $catalog, is
            driver specific.  If the driver doesn’t support catalogs and/or
            schemas, it may ignore these criteria.
 
            The statement handle returned has the following fields in the order
            shown below.  Because ODBC never includes unique keys, they define
            different columns in the result set than SQL/CLI. SQL/CLI column
            names are shown in parentheses.
 
            PKTABLE_CAT    ( UK_TABLE_CAT      ): The primary (unique) key ta‐
            ble catalog identifier.  This field is NULL ("undef") if not appli‐
            cable to the data source, which is often the case.  This field is
            empty if not applicable to the table.
 
            PKTABLE_SCHEM  ( UK_TABLE_SCHEM    ): The primary (unique) key ta‐
            ble schema identifier.  This field is NULL ("undef") if not appli‐
            cable to the data source, and empty if not applicable to the table.
 
            PKTABLE_NAME   ( UK_TABLE_NAME     ): The primary (unique) key ta‐
            ble identifier.
 
            PKCOLUMN_NAME  (UK_COLUMN_NAME    ): The primary (unique) key col‐
            umn identifier.
 
            FKTABLE_CAT    ( FK_TABLE_CAT      ): The foreign key table catalog
            identifier.  This field is NULL ("undef") if not applicable to the
            data source, which is often the case.  This field is empty if not
            applicable to the table.
 
            FKTABLE_SCHEM  ( FK_TABLE_SCHEM    ): The foreign key table schema
            identifier.  This field is NULL ("undef") if not applicable to the
            data source, and empty if not applicable to the table.
 
            FKTABLE_NAME   ( FK_TABLE_NAME     ): The foreign key table identi‐
            fier.
 
            FKCOLUMN_NAME  ( FK_COLUMN_NAME    ): The foreign key column iden‐
            tifier.
 
            KEY_SEQ        ( ORDINAL_POSITION  ): The column sequence number
            (starting with 1).
 
            UPDATE_RULE    ( UPDATE_RULE       ): The referential action for
            the UPDATE rule.  The following codes are defined:
 
              CASCADE              0
              RESTRICT             1
              SET NULL             2
              NO ACTION            3
              SET DEFAULT          4
 
            DELETE_RULE    ( DELETE_RULE       ): The referential action for
            the DELETE rule.  The codes are the same as for UPDATE_RULE.
 
            FK_NAME        ( FK_NAME           ): The foreign key name.
 
            PK_NAME        ( UK_NAME           ): The primary (unique) key
            name.
 
            DEFERRABILITY  ( DEFERABILITY      ): The deferrability of the for‐
            eign key constraint.  The following codes are defined:
 
              INITIALLY DEFERRED   5
              INITIALLY IMMEDIATE  6
              NOT DEFERRABLE       7
 
                           ( UNIQUE_OR_PRIMARY ): This column is necessary if a
            driver includes all candidate (i.e. primary and alternate) keys in
            the result set (as specified by SQL/CLI).  The value of this column
            is UNIQUE if the foreign key references an alternate key and PRI‐
            MARY if the foreign key references a primary key, or it may be
            undefined if the driver doesn’t have access to the information.
 
            See also "Catalog Methods" and "Standards Reference Information".
 
        "statistics_info"
            Warning: This method is experimental and may change.
 
              $sth = $dbh->statistics_info( $catalog, $schema, $table, $unique_only, $quick );
 
            Returns an active statement handle that can be used to fetch sta‐
            tistical information about a table and its indexes.
 
            The arguments don’t accept search patterns (unlike "table_info").
 
            If the boolean argument $unique_only is true, only UNIQUE indexes
            will be returned in the result set, otherwise all indexes will be
            returned.
 
            If the boolean argument $quick is set, the actual statistical
            information columns (CARDINALITY and PAGES) will only be returned
            if they are readily available from the server, and might not be
            current.  Some databases may return stale statistics or no statis‐
            tics at all with this flag set.
 
            For example:
 
              $sth = $dbh->statistics_info( undef, $user, ’foo’, 1, 1 );
              $data = $sth->fetchall_arrayref;
 
            The statement handle will return at most one row per column name
            per index, plus at most one row for the entire table itself,
            ordered by NON_UNIQUE, TYPE, INDEX_QUALIFIER, INDEX_NAME, and ORDI‐
            NAL_POSITION.
 
            Note: The support for the selection criteria, such as $catalog, is
            driver specific.  If the driver doesn’t support catalogs and/or
            schemas, it may ignore these criteria.
 
            The statement handle returned has at least the following fields in
            the order shown below. Other fields, after these, may also be
            present.
 
            TABLE_CAT: The catalog identifier.  This field is NULL ("undef") if
            not applicable to the data source, which is often the case.  This
            field is empty if not applicable to the table.
 
            TABLE_SCHEM: The schema identifier.  This field is NULL ("undef")
            if not applicable to the data source, and empty if not applicable
            to the table.
 
            TABLE_NAME: The table identifier.
 
            NON_UNIQUE: Unique index indicator.  Returns 0 for unique indexes,
            1 for non-unique indexes
 
            INDEX_QUALIFIER: Index qualifier identifier.  The identifier that
            is used to qualify the index name when doing a "DROP INDEX"; NULL
            ("undef") is returned if an index qualifier is not supported by the
            data source.  If a non-NULL (defined) value is returned in this
            column, it must be used to qualify the index name on a "DROP INDEX"
            statement; otherwise, the TABLE_SCHEM should be used to qualify the
            index name.
 
            INDEX_NAME: The index identifier.
 
            TYPE: The type of information being returned.  Can be any of the
            following values: ’table’, ’btree’, ’clustered’, ’content’,
            ’hashed’, or ’other’.
 
            In the case that this field is ’table’, all fields other than TA‐
            BLE_CAT, TABLE_SCHEM, TABLE_NAME, TYPE, CARDINALITY, and PAGES will
            be NULL ("undef").
 
            ORDINAL_POSITION: Column sequence number (starting with 1).
 
            COLUMN_NAME: The column identifier.
 
            ASC_OR_DESC: Column sort sequence.  "A" for Ascending, "D" for
            Descending, or NULL ("undef") if not supported for this index.
 
            CARDINALITY: Cardinality of the table or index.  For indexes, this
            is the number of unique values in the index.  For tables, this is
            the number of rows in the table.  If not supported, the value will
            be NULL ("undef").
 
            PAGES: Number of storage pages used by this table or index.  If not
            supported, the value will be NULL ("undef").
 
            FILTER_CONDITION: The index filter condition as a string.  If the
            index is not a filtered index, or it cannot be determined whether
            the index is a filtered index, this value is NULL ("undef").  If
            the index is a filtered index, but the filter condition cannot be
            determined, this value is the empty string ’’.  Otherwise it will
            be the literal filter condition as a string, such as "SALARY <=
            4500".
 
            See also "Catalog Methods" and "Standards Reference Information".
 
        "tables"
              @names = $dbh->tables( $catalog, $schema, $table, $type );
              @names = $dbh->tables;        # deprecated
 
            Simple interface to table_info(). Returns a list of matching table
            names, possibly including a catalog/schema prefix.
 
            See "table_info" for a description of the parameters.
 
            If "$dbh->get_info(29)" returns true (29 is SQL_IDENTI‐
            FIER_QUOTE_CHAR) then the table names are constructed and quoted by
            "quote_identifier" to ensure they are usable even if they contain
            whitespace or reserved words etc. This means that the table names
            returned will include quote characters.
 
        "type_info_all"
              $type_info_all = $dbh->type_info_all;
 
            Returns a reference to an array which holds information about each
            data type variant supported by the database and driver. The array
            and its contents should be treated as read-only.
 
            The first item is a reference to an ’index’ hash of "Name =">
            "Index" pairs.  The items following that are references to arrays,
            one per supported data type variant. The leading index hash defines
            the names and order of the fields within the arrays that follow it.
            For example:
 
              $type_info_all = [
                {   TYPE_NAME         => 0,
                    DATA_TYPE         => 1,
                    COLUMN_SIZE       => 2,     # was PRECISION originally
                    LITERAL_PREFIX    => 3,
                    LITERAL_SUFFIX    => 4,
                    CREATE_PARAMS     => 5,
                    NULLABLE          => 6,
                    CASE_SENSITIVE    => 7,
                    SEARCHABLE        => 8,
                    UNSIGNED_ATTRIBUTE=> 9,
                    FIXED_PREC_SCALE  => 10,    # was MONEY originally
                    AUTO_UNIQUE_VALUE => 11,    # was AUTO_INCREMENT originally
                    LOCAL_TYPE_NAME   => 12,
                    MINIMUM_SCALE     => 13,
                    MAXIMUM_SCALE     => 14,
                    SQL_DATA_TYPE     => 15,
                    SQL_DATETIME_SUB  => 16,
                    NUM_PREC_RADIX    => 17,
                    INTERVAL_PRECISION=> 18,
                },
                [ ’VARCHAR’, SQL_VARCHAR,
                    undef, "’","’", undef,0, 1,1,0,0,0,undef,1,255, undef
                ],
                [ ’INTEGER’, SQL_INTEGER,
                    undef,  "", "", undef,0, 0,1,0,0,0,undef,0,  0, 10
                ],
              ];
 
            More than one row may have the same value in the "DATA_TYPE" field
            if there are different ways to spell the type name and/or there are
            variants of the type with different attributes (e.g., with and
            without "AUTO_UNIQUE_VALUE" set, with and without
            "UNSIGNED_ATTRIBUTE", etc).
 
            The rows are ordered by "DATA_TYPE" first and then by how closely
            each type maps to the corresponding ODBC SQL data type, closest
            first.
 
            The meaning of the fields is described in the documentation for the
            "type_info" method.
 
            An ’index’ hash is provided so you don’t need to rely on index val‐
            ues defined above.  However, using DBD::ODBC with some old ODBC
            drivers may return older names, shown as comments in the example
            above.  Another issue with the index hash is that the lettercase of
            the keys is not defined. It is usually uppercase, as show here, but
            drivers may return names with any lettercase.
 
            Drivers are also free to return extra driver-specific columns of
            information - though it’s recommended that they start at column
            index 50 to leave room for expansion of the DBI/ODBC specification.
 
            The type_info_all() method is not normally used directly.  The
            "type_info" method provides a more usable and useful interface to
            the data.
 
        "type_info"
              @type_info = $dbh->type_info($data_type);
 
            Returns a list of hash references holding information about one or
            more variants of $data_type. The list is ordered by "DATA_TYPE"
            first and then by how closely each type maps to the corresponding
            ODBC SQL data type, closest first.  If called in a scalar context
            then only the first (best) element is returned.
 
            If $data_type is undefined or "SQL_ALL_TYPES", then the list will
            contain hashes for all data type variants supported by the database
            and driver.
 
            If $data_type is an array reference then "type_info" returns the
            information for the first type in the array that has any matches.
 
            The keys of the hash follow the same letter case conventions as the
            rest of the DBI (see "Naming Conventions and Name Space"). The fol‐
            lowing uppercase items should always exist, though may be undef:
 
            TYPE_NAME (string)
                Data type name for use in CREATE TABLE statements etc.
 
            DATA_TYPE (integer)
                SQL data type number.
 
            COLUMN_SIZE (integer)
                For numeric types, this is either the total number of digits
                (if the NUM_PREC_RADIX value is 10) or the total number of bits
                allowed in the column (if NUM_PREC_RADIX is 2).
 
                For string types, this is the maximum size of the string in
                characters.
 
                For date and interval types, this is the maximum number of
                characters needed to display the value.
 
            LITERAL_PREFIX (string)
                Characters used to prefix a literal. A typical prefix is ""’""
                for characters, or possibly ""0x"" for binary values passed as
                hexadecimal.  NULL ("undef") is returned for data types for
                which this is not applicable.
 
            LITERAL_SUFFIX (string)
                Characters used to suffix a literal. Typically ""’"" for char‐
                acters.  NULL ("undef") is returned for data types where this
                is not applicable.
 
            CREATE_PARAMS (string)
                Parameter names for data type definition. For example, "CRE‐
                ATE_PARAMS" for a "DECIMAL" would be ""precision,scale"" if the
                DECIMAL type should be declared as "DECIMAL("precision,scale")"
                where precision and scale are integer values.  For a "VARCHAR"
                it would be ""max length"".  NULL ("undef") is returned for
                data types for which this is not applicable.
 
            NULLABLE (integer)
                Indicates whether the data type accepts a NULL value: 0 or an
                empty string = no, 1 = yes, 2 = unknown.
 
            CASE_SENSITIVE (boolean)
                Indicates whether the data type is case sensitive in collations
                and comparisons.
 
            SEARCHABLE (integer)
                Indicates how the data type can be used in a WHERE clause, as
                follows:
 
                  0 - Cannot be used in a WHERE clause
                  1 - Only with a LIKE predicate
                  2 - All comparison operators except LIKE
                  3 - Can be used in a WHERE clause with any comparison operator
 
            UNSIGNED_ATTRIBUTE (boolean)
                Indicates whether the data type is unsigned.  NULL ("undef") is
                returned for data types for which this is not applicable.
 
            FIXED_PREC_SCALE (boolean)
                Indicates whether the data type always has the same precision
                and scale (such as a money type).  NULL ("undef") is returned
                for data types for which this is not applicable.
 
            AUTO_UNIQUE_VALUE (boolean)
                Indicates whether a column of this data type is automatically
                set to a unique value whenever a new row is inserted.  NULL
                ("undef") is returned for data types for which this is not
                applicable.
 
            LOCAL_TYPE_NAME (string)
                Localized version of the "TYPE_NAME" for use in dialog with
                users.  NULL ("undef") is returned if a localized name is not
                available (in which case "TYPE_NAME" should be used).
 
            MINIMUM_SCALE (integer)
                The minimum scale of the data type. If a data type has a fixed
                scale, then "MAXIMUM_SCALE" holds the same value.  NULL
                ("undef") is returned for data types for which this is not
                applicable.
 
            MAXIMUM_SCALE (integer)
                The maximum scale of the data type. If a data type has a fixed
                scale, then "MINIMUM_SCALE" holds the same value.  NULL
                ("undef") is returned for data types for which this is not
                applicable.
 
            SQL_DATA_TYPE (integer)
                This column is the same as the "DATA_TYPE" column, except for
                interval and datetime data types.  For interval and datetime
                data types, the "SQL_DATA_TYPE" field will return "SQL_INTER‐
                VAL" or "SQL_DATETIME", and the "SQL_DATETIME_SUB" field below
                will return the subcode for the specific interval or datetime
                data type. If this field is NULL, then the driver does not sup‐
                port or report on interval or datetime subtypes.
 
            SQL_DATETIME_SUB (integer)
                For interval or datetime data types, where the "SQL_DATA_TYPE"
                field above is "SQL_INTERVAL" or "SQL_DATETIME", this field
                will hold the subcode for the specific interval or datetime
                data type.  Otherwise it will be NULL ("undef").
 
                Although not mentioned explicitly in the standards, it seems
                there is a simple relationship between these values:
 
                  DATA_TYPE == (10 * SQL_DATA_TYPE) + SQL_DATETIME_SUB
 
            NUM_PREC_RADIX (integer)
                The radix value of the data type. For approximate numeric
                types, "NUM_PREC_RADIX" contains the value 2 and "COLUMN_SIZE"
                holds the number of bits. For exact numeric types,
                "NUM_PREC_RADIX" contains the value 10 and "COLUMN_SIZE" holds
                the number of decimal digits. NULL ("undef") is returned either
                for data types for which this is not applicable or if the
                driver cannot report this information.
 
            INTERVAL_PRECISION (integer)
                The interval leading precision for interval types. NULL is
                returned either for data types for which this is not applicable
                or if the driver cannot report this information.
 
            For example, to find the type name for the fields in a select
            statement you can do:
 
              @names = map { scalar $dbh->type_info($_)->{TYPE_NAME} } @{ $sth->{TYPE} }
 
            Since DBI and ODBC drivers vary in how they map their types into
            the ISO standard types you may need to search for more than one
            type.  Here’s an example looking for a usable type to store a date:
 
              $my_date_type = $dbh->type_info( [ SQL_DATE, SQL_TIMESTAMP ] );
 
            Similarly, to more reliably find a type to store small integers,
            you could use a list starting with "SQL_SMALLINT", "SQL_INTEGER",
            "SQL_DECIMAL", etc.
 
            See also "Standards Reference Information".
 
        "quote"
              $sql = $dbh->quote($value);
              $sql = $dbh->quote($value, $data_type);
 
            Quote a string literal for use as a literal value in an SQL state‐
            ment, by escaping any special characters (such as quotation marks)
            contained within the string and adding the required type of outer
            quotation marks.
 
              $sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
                            $dbh->quote("Don’t");
 
            For most database types, quote would return ’Don’’t’ (including the
            outer quotation marks).
 
            An undefined $value value will be returned as the string "NULL"
            (without single quotation marks) to match how NULLs are represented
            in SQL.
 
            If $data_type is supplied, it is used to try to determine the
            required quoting behaviour by using the information returned by
            "type_info".  As a special case, the standard numeric types are
            optimized to return $value without calling "type_info".
 
            Quote will probably not be able to deal with all possible input
            (such as binary data or data containing newlines), and is not
            related in any way with escaping or quoting shell meta-characters.
 
            It is valid for the quote() method to return an SQL expression that
            evaluates to the desired string. For example:
 
              $quoted = $dbh->quote("one\ntwo\0three")
 
            may return something like:
 
              CONCAT(’one’, CHAR(12), ’two’, CHAR(0), ’three’)
 
            The quote() method should not be used with "Placeholders and Bind
            Values".
 
        "quote_identifier"
              $sql = $dbh->quote_identifier( $name );
              $sql = $dbh->quote_identifier( $catalog, $schema, $table, \%attr );
 
            Quote an identifier (table name etc.) for use in an SQL statement,
            by escaping any special characters (such as double quotation marks)
            it contains and adding the required type of outer quotation marks.
 
            Undefined names are ignored and the remainder are quoted and then
            joined together, typically with a dot (".") character. For example:
 
              $id = $dbh->quote_identifier( undef, ’Her schema’, ’My table’ );
 
            would, for most database types, return "Her schema"."My table"
            (including all the double quotation marks).
 
            If three names are supplied then the first is assumed to be a cata‐
            log name and special rules may be applied based on what "get_info"
            returns for SQL_CATALOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCA‐
            TION (114).  For example, for Oracle:
 
              $id = $dbh->quote_identifier( ’link’, ’schema’, ’table’ );
 
            would return "schema"."table"@"link".
 
        "take_imp_data"
              $imp_data = $dbh->take_imp_data;
 
            Leaves the $dbh in an almost dead, zombie-like, state and returns a
            binary string of raw implementation data from the driver which
            describes the current database connection. Effectively it detaches
            the underlying database API connection data from the DBI handle.
            After calling take_imp_data(), all other methods except "DESTROY"
            will generate a warning and return undef.
 
            Why would you want to do this? You don’t, forget I even mentioned
            it.  Unless, that is, you’re implementing something advanced like a
            multi-threaded connection pool. See DBI::Pool.
 
            The returned $imp_data can be passed as a "dbi_imp_data" attribute
            to a later connect() call, even in a separate thread in the same
            process, where the driver can use it to ’adopt’ the existing con‐
            nection that the implementation data was taken from.
 
            Some things to keep in mind...
 
            * the $imp_data holds the only reference to the underlying database
            API connection data. That connection is still ’live’ and won’t be
            cleaned up properly unless the $imp_data is used to create a new
            $dbh which is then allowed to disconnect() normally.
 
            * using the same $imp_data to create more than one other new $dbh
            at a time may well lead to unpleasant problems. Don’t do that.
 
            Any child statement handles are effectively destroyed when
            take_imp_data() is called.
 
            The "take_imp_data" method was added in DBI 1.36 but wasn’t useful
            till 1.49.
 
        Database Handle Attributes
 
        This section describes attributes specific to database handles.
 
        Changes to these database handle attributes do not affect any other
        existing or future database handles.
 
        Attempting to set or get the value of an unknown attribute generates a
        warning, except for private driver-specific attributes (which all have
        names starting with a lowercase letter).
 
        Example:
 
          $h->{AutoCommit} = ...;       # set/write
          ... = $h->{AutoCommit};       # get/read
 
        "AutoCommit"  (boolean)
            If true, then database changes cannot be rolled-back (undone).  If
            false, then database changes automatically occur within a "transac‐
            tion", which must either be committed or rolled back using the
            "commit" or "rollback" methods.
 
            Drivers should always default to "AutoCommit" mode (an unfortunate
            choice largely forced on the DBI by ODBC and JDBC conventions.)
 
            Attempting to set "AutoCommit" to an unsupported value is a fatal
            error.  This is an important feature of the DBI. Applications that
            need full transaction behaviour can set "$dbh->{AutoCommit} = 0"
            (or set "AutoCommit" to 0 via "connect") without having to check
            that the value was assigned successfully.
 
            For the purposes of this description, we can divide databases into
            three categories:
 
              Databases which don’t support transactions at all.
              Databases in which a transaction is always active.
              Databases in which a transaction must be explicitly started (C<’BEGIN WORK’>).
 
            * Databases which don     t support transactions at all
 
            For these databases, attempting to turn "AutoCommit" off is a fatal
            error.  "commit" and "rollback" both issue warnings about being
            ineffective while "AutoCommit" is in effect.
 
            * Databases in which a transaction is always active
 
            These are typically mainstream commercial relational databases with
            "ANSI standard" transaction behaviour.  If "AutoCommit" is off,
            then changes to the database won’t have any lasting effect unless
            "commit" is called (but see also "disconnect"). If "rollback" is
            called then any changes since the last commit are undone.
 
            If "AutoCommit" is on, then the effect is the same as if the DBI
            called "commit" automatically after every successful database oper‐
            ation. So calling "commit" or "rollback" explicitly while "AutoCom‐
            mit" is on would be ineffective because the changes would have
            already been commited.
 
            Changing "AutoCommit" from off to on will trigger a "commit".
 
            For databases which don’t support a specific auto-commit mode, the
            driver has to commit each statement automatically using an explicit
            "COMMIT" after it completes successfully (and roll it back using an
            explicit "ROLLBACK" if it fails).  The error information reported
            to the application will correspond to the statement which was exe‐
            cuted, unless it succeeded and the commit or rollback failed.
 
            * Databases in which a transaction must be explicitly started
 
            For these databases, the intention is to have them act like
            databases in which a transaction is always active (as described
            above).
 
            To do this, the driver will automatically begin an explicit trans‐
            action when "AutoCommit" is turned off, or after a "commit" or
            "rollback" (or when the application issues the next database opera‐
            tion after one of those events).
 
            In this way, the application does not have to treat these databases
            as a special case.
 
            See "commit", "disconnect" and "Transactions" for other important
            notes about transactions.
 
        "Driver"  (handle)
            Holds the handle of the parent driver. The only recommended use for
            this is to find the name of the driver using:
 
              $dbh->{Driver}->{Name}
 
        "Name"  (string)
            Holds the "name" of the database. Usually (and recommended to be)
            the same as the ""dbi:DriverName:..."" string used to connect to
            the database, but with the leading ""dbi:DriverName:"" removed.
 
        "Statement"  (string, read-only)
            Returns the statement string passed to the most recent "prepare"
            method called in this database handle, even if that method failed.
            This is especially useful where "RaiseError" is enabled and the
            exception handler checks $@ and sees that a ’prepare’ method call
            failed.
 
        "RowCacheSize"  (integer)
            A hint to the driver indicating the size of the local row cache
            that the application would like the driver to use for future
            "SELECT" statements.  If a row cache is not implemented, then set‐
            ting "RowCacheSize" is ignored and getting the value returns
            "undef".
 
            Some "RowCacheSize" values have special meaning, as follows:
 
              0 - Automatically determine a reasonable cache size for each C<SELECT>
              1 - Disable the local row cache
             >1 - Cache this many rows
             <0 - Cache as many rows that will fit into this much memory for each C<SELECT>.
 
            Note that large cache sizes may require a very large amount of mem‐
            ory (cached rows * maximum size of row). Also, a large cache will
            cause a longer delay not only for the first fetch, but also when‐
            ever the cache needs refilling.
 
            See also the "RowsInCache" statement handle attribute.
 
        "Username"  (string)
            Returns the username used to connect to the database.
        This section lists the methods and attributes associated with DBI
        statement handles.
 
        Statement Handle Methods
 
        The DBI defines the following methods for use on DBI statement handles:
 
        "bind_param"
              $sth->bind_param($p_num, $bind_value)
              $sth->bind_param($p_num, $bind_value, \%attr)
              $sth->bind_param($p_num, $bind_value, $bind_type)
 
            The "bind_param" method takes a copy of $bind_value and associates
            it (binds it) with a placeholder, identified by $p_num, embedded in
            the prepared statement. Placeholders are indicated with question
            mark character ("?"). For example:
 
              $dbh->{RaiseError} = 1;        # save having to check each method call
              $sth = $dbh->prepare("SELECT name, age FROM people WHERE name LIKE ?");
              $sth->bind_param(1, "John%");  # placeholders are numbered from 1
              $sth->execute;
              DBI::dump_results($sth);
 
            See "Placeholders and Bind Values" for more information.
 
            Data Types for Placeholders
 
            The "\%attr" parameter can be used to hint at the data type the
            placeholder should have. This is rarely needed. Typically, the
            driver is only interested in knowing if the placeholder should be
            bound as a number or a string.
 
              $sth->bind_param(1, $value, { TYPE => SQL_INTEGER });
 
            As a short-cut for the common case, the data type can be passed
            directly, in place of the "\%attr" hash reference. This example is
            equivalent to the one above:
 
              $sth->bind_param(1, $value, SQL_INTEGER);
 
            The "TYPE" value indicates the standard (non-driver-specific) type
            for this parameter. To specify the driver-specific type, the driver
            may support a driver-specific attribute, such as "{ ora_type => 97
            }".
 
            The SQL_INTEGER and other related constants can be imported using
 
              use DBI qw(:sql_types);
 
            See "DBI Constants" for more information.
 
            The data type for a placeholder cannot be changed after the first
            "bind_param" call. In fact the whole \%attr parameter is ’sticky’
            in the sense that a driver only needs to consider the \%attr param‐
            eter for the first call, for a given $sth and parameter. After that
            the driver may ignore the \%attr parameter for that placeholder.
 
            Perl only has string and number scalar data types. All database
            types that aren’t numbers are bound as strings and must be in a
            format the database will understand except where the bind_param()
            TYPE attribute specifies a type that implies a particular format.
            For example, given:
 
              $sth->bind_param(1, $value, SQL_DATETIME);
 
            the driver should expect $value to be in the ODBC standard
            SQL_DATETIME format, which is ’YYYY-MM-DD HH:MM:SS’. Similarly for
            SQL_DATE, SQL_TIME etc.
 
            As an alternative to specifying the data type in the "bind_param"
            call, you can let the driver pass the value as the default type
            ("VARCHAR").  You can then use an SQL function to convert the type
            within the statement.  For example:
 
              INSERT INTO price(code, price) VALUES (?, CONVERT(MONEY,?))
 
            The "CONVERT" function used here is just an example. The actual
            function and syntax will vary between different databases and is
            non-portable.
 
            See also "Placeholders and Bind Values" for more information.
 
        "bind_param_inout"
              $rc = $sth->bind_param_inout($p_num, \$bind_value, $max_len)  or die $sth->errstr;
              $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, \%attr)     or ...
              $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, $bind_type) or ...
 
            This method acts like "bind_param", but also enables values to be
            updated by the statement. The statement is typically a call to a
            stored procedure. The $bind_value must be passed as a reference to
            the actual value to be used.
 
            Note that unlike "bind_param", the $bind_value variable is not
            copied when "bind_param_inout" is called. Instead, the value in the
            variable is read at the time "execute" is called.
 
            The additional $max_len parameter specifies the minimum amount of
            memory to allocate to $bind_value for the new value. If the value
            returned from the database is too big to fit, then the execution
            should fail. If unsure what value to use, pick a generous length,
            i.e., a length larger than the longest value that would ever be
            returned.  The only cost of using a larger value than needed is
            wasted memory.
 
            Undefined values or "undef" are used to indicate null values.  See
            also "Placeholders and Bind Values" for more information.
 
        "bind_param_array"
              $rc = $sth->bind_param_array($p_num, $array_ref_or_value)
              $rc = $sth->bind_param_array($p_num, $array_ref_or_value, \%attr)
              $rc = $sth->bind_param_array($p_num, $array_ref_or_value, $bind_type)
 
            The "bind_param_array" method is used to bind an array of values to
            a placeholder embedded in the prepared statement which is to be
            executed with "execute_array". For example:
 
              $dbh->{RaiseError} = 1;        # save having to check each method call
              $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name, dept) VALUES(?, ?, ?)");
              $sth->bind_param_array(1, [ ’John’, ’Mary’, ’Tim’ ]);
              $sth->bind_param_array(2, [ ’Booth’, ’Todd’, ’Robinson’ ]);
              $sth->bind_param_array(3, "SALES"); # scalar will be reused for each row
              $sth->execute_array( { ArrayTupleStatus => \my @tuple_status } );
 
            The %attr ($bind_type) argument is the same as defined for
            "bind_param".  Refer to "bind_param" for general details on using
            placeholders.
 
            (Note that bind_param_array() can not be used to expand a place‐
            holder into a list of values for a statement like "SELECT foo WHERE
            bar IN (?)".  A placeholder can only ever represent one value per
            execution.)
 
            Scalar values, including "undef", may also be bound by
            "bind_param_array". In which case the same value will be used for
            each "execute" call. Driver-specific implementations may behave
            differently, e.g., when binding to a stored procedure call, some
            databases may permit mixing scalars and arrays as arguments.
 
            The default implementation provided by DBI (for drivers that have
            not implemented array binding) is to iteratively call "execute" for
            each parameter tuple provided in the bound arrays.  Drivers may
            provide more optimized implementations using whatever bulk opera‐
            tion support the database API provides. The default driver
            behaviour should match the default DBI behaviour, but always
            consult your driver documentation as there may be driver specific
            issues to consider.
 
            Note that the default implementation currently only supports non-
            data returning statements (INSERT, UPDATE, but not SELECT). Also,
            "bind_param_array" and "bind_param" cannot be mixed in the same
            statement execution, and "bind_param_array" must be used with "exe‐
            cute_array"; using "bind_param_array" will have no effect for "exe‐
            cute".
 
            The "bind_param_array" method was added in DBI 1.22.
 
        "execute"
              $rv = $sth->execute                or die $sth->errstr;
              $rv = $sth->execute(@bind_values)  or die $sth->errstr;
 
            Perform whatever processing is necessary to execute the prepared
            statement.  An "undef" is returned if an error occurs.  A success‐
            ful "execute" always returns true regardless of the number of rows
            affected, even if it’s zero (see below). It is always important to
            check the return status of "execute" (and most other DBI methods)
            for errors if you’re not using "RaiseError".
 
            For a non-"SELECT" statement, "execute" returns the number of rows
            affected, if known. If no rows were affected, then "execute"
            returns "0E0", which Perl will treat as 0 but will regard as true.
            Note that it is not an error for no rows to be affected by a state‐
            ment. If the number of rows affected is not known, then "execute"
            returns -1.
 
            For "SELECT" statements, execute simply "starts" the query within
            the database engine. Use one of the fetch methods to retrieve the
            data after calling "execute".  The "execute" method does not return
            the number of rows that will be returned by the query (because most
            databases can’t tell in advance), it simply returns a true value.
 
            You can tell if the statement was a "SELECT" statement by checking
            if "$sth->{NUM_OF_FIELDS}" is greater than zero after calling "exe‐
            cute".
 
            If any arguments are given, then "execute" will effectively call
            "bind_param" for each value before executing the statement.  Values
            bound in this way are usually treated as "SQL_VARCHAR" types unless
            the driver can determine the correct type (which is rare), or
            unless "bind_param" (or "bind_param_inout") has already been used
            to specify the type.
 
            If execute() is called on a statement handle that’s still active
            ($sth->{Active} is true) then it should effectively call finish()
            to tidy up the previous execution results before starting this new
            execution.
 
        "execute_array"
              $tuples = $sth->execute_array(\%attr) or die $sth->errstr;
              $tuples = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
 
              ($tuples, $rows) = $sth->execute_array(\%attr) or die $sth->errstr;
              ($tuples, $rows) = $sth->execute_array(\%attr, @bind_values) or die $sth->errstr;
 
            Execute the prepared statement once for each parameter tuple (group
            of values) provided either in the @bind_values, or by prior calls
            to "bind_param_array", or via a reference passed in \%attr.
 
            When called in scalar context the execute_array() method returns
            the number of tuples executed, or "undef" if an error occured.
            Like execute(), a successful execute_array() always returns true
            regardless of the number of tuples executed, even if it’s zero. If
            there were any errors the ArrayTupleStatus array can be used to
            discover which tuples failed and with what errors.
 
            When called in list context the execute_array() method returns two
            scalars; $tuples is the same as calling execute_array() in scalar
            context and $rows is the sum of the number of rows affected for
            each tuple, if available or -1 if the driver cannot determine this.
            If you are doing an update operation the returned rows affected may
            not be what you expect if, for instance, one or more of the tuples
            affected the same row multiple times.  Some drivers may not yet
            support list context, in which case $rows will be undef, or may not
            be able to provide the number of rows affected when performing this
            batch operation, in which case $rows will be -1.
 
            Bind values for the tuples to be executed may be supplied row-wise
            by an "ArrayTupleFetch" attribute, or else column-wise in the
            @bind_values argument, or else column-wise by prior calls to
            "bind_param_array".
 
            Where column-wise binding is used (via the @bind_values argument or
            calls to bind_param_array()) the maximum number of elements in any
            one of the bound value arrays determines the number of tuples exe‐
            cuted. Placeholders with fewer values in their parameter arrays are
            treated as if padded with undef (NULL) values.
 
            If a scalar value is bound, instead of an array reference, it is
            treated as a variable length array with all elements having the
            same value. It’s does not influence the number of tuples executed,
            so if all bound arrays have zero elements then zero tuples will be
            executed. If all bound values are scalars then one tuple will be
            executed, making execute_array() act just like execute().
 
            The "ArrayTupleFetch" attribute can be used to specify a reference
            to a subroutine that will be called to provide the bind values for
            each tuple execution. The subroutine should return an reference to
            an array which contains the appropriate number of bind values, or
            return an undef if there is no more data to execute.
 
            As a convienience, the "ArrayTupleFetch" attribute can also be used
            to specify a statement handle. In which case the
            fetchrow_arrayref() method will be called on the given statement
            handle in order to provide the bind values for each tuple execu‐
            tion.
 
            The values specified via bind_param_array() or the @bind_values
            parameter may be either scalars, or arrayrefs.  If any @bind_values
            are given, then "execute_array" will effectively call
            "bind_param_array" for each value before executing the statement.
            Values bound in this way are usually treated as "SQL_VARCHAR" types
            unless the driver can determine the correct type (which is rare),
            or unless "bind_param", "bind_param_inout", "bind_param_array", or
            "bind_param_inout_array" has already been used to specify the type.
            See "bind_param_array" for details.
 
            The "ArrayTupleStatus" attribute can be used to specify a reference
            to an array which will receive the execute status of each executed
            parameter tuple. Note the "ArrayTupleStatus" attribute was manda‐
            tory until DBI 1.38.
 
            For tuples which are successfully executed, the element at the same
            ordinal position in the status array is the resulting rowcount.  If
            the execution of a tuple causes an error, then the corresponding
            status array element will be set to a reference to an array con‐
            taining the error code and error string set by the failed execu‐
            tion.
 
            If any tuple execution returns an error, "execute_array" will
            return "undef". In that case, the application should inspect the
            status array to determine which parameter tuples failed.  Some
            databases may not continue executing tuples beyond the first fail‐
            ure. In this case the status array will either hold fewer elements,
            or the elements beyond the failure will be undef.
 
            If all parameter tuples are successfully executed, "execute_array"
            returns the number tuples executed.  If no tuples were executed,
            then execute_array() returns "0E0", just like execute() does, which
            Perl will treat as 0 but will regard as true.
 
            For example:
 
              $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name) VALUES (?, ?)");
              my $tuples = $sth->execute_array(
                  { ArrayTupleStatus => \my @tuple_status },
                  \@first_names,
                  \@last_names,
              );
              if ($tuples) {
                  print "Successfully inserted $tuples records\n";
              }
              else {
                  for my $tuple (0..@last_names-1) {
                      my $status = $tuple_status[$tuple];
                      $status = [0, "Skipped"] unless defined $status;
                      next unless ref $status;
                      printf "Failed to insert (%s, %s): %s\n",
                          $first_names[$tuple], $last_names[$tuple], $status->[1];
                  }
              }
 
            Support for data returning statements such as SELECT is driver-spe‐
            cific and subject to change. At present, the default implementation
            provided by DBI only supports non-data returning statements.
 
            Transaction semantics when using array binding are driver and
            database specific.  If "AutoCommit" is on, the default DBI imple‐
            mentation will cause each parameter tuple to be inidividually com‐
            mitted (or rolled back in the event of an error). If "AutoCommit"
            is off, the application is responsible for explicitly committing
            the entire set of bound parameter tuples.  Note that different
            drivers and databases may have different behaviours when some
            parameter tuples cause failures. In some cases, the driver or
            database may automatically rollback the effect of all prior parame‐
            ter tuples that succeeded in the transaction; other drivers or
            databases may retain the effect of prior successfully executed
            parameter tuples. Be sure to check your driver and database for its
            specific behaviour.
 
            Note that, in general, performance will usually be better with
            "AutoCommit" turned off, and using explicit "commit" after each
            "execute_array" call.
 
            The "execute_array" method was added in DBI 1.22, and ArrayTuple‐
            Fetch was added in 1.36.
 
        "execute_for_fetch"
              $tuples = $sth->execute_for_fetch($fetch_tuple_sub);
              $tuples = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
 
              ($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub);
              ($tuples, $rows) = $sth->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
 
            The execute_for_fetch() method is used to perform bulk operations
            and is most often used via the execute_array() method, not
            directly.
 
            The fetch subroutine, referenced by $fetch_tuple_sub, is expected
            to return a reference to an array (known as a ’tuple’) or undef.
 
            The execute_for_fetch() method calls $fetch_tuple_sub, without any
            parameters, until it returns a false value. Each tuple returned is
            used to provide bind values for an $sth->execute(@$tuple) call.
 
            In scalar context execute_for_fetch() returns "undef" if there were
            any errors and the number of tuples executed otherwise. Like exe‐
            cute() and execute_array() a zero is returned as "0E0" so exe‐
            cute_for_fetch() is only false on error.  If there were any errors
            the @tuple_status array can be used to discover which tuples failed
            and with what errors.
 
            When called in list context execute_for_fetch() returns two
            scalars; $tuples is the same as calling execute_for_fetch() in
            scalar context and $rows is the sum of the number of rows affected
            for each tuple, if available or -1 if the driver cannot determine
            this.  If you are doing an update operation the returned rows
            affected may not be what you expect if, for instance, one or more
            of the tuples affected the same row multiple times.  Some drivers
            may not yet support list context, in which case $rows will be
            undef, or may not be able to provide the number of rows affected
            when performing this batch operation, in which case $rows will be
            -1.
 
            If \@tuple_status is passed then the execute_for_fetch method uses
            it to return status information. The tuple_status array holds one
            element per tuple. If the corresponding execute() did not fail then
            the element holds the return value from execute(), which is typi‐
            cally a row count. If the execute() did fail then the element holds
            a reference to an array containing ($sth->err, $sth->errstr,
            $sth->state).
 
            If the driver detects an error that it knows means no further
            tuples can be executed then it may return, with an error status,
            even though $fetch_tuple_sub may still have more tuples to be exe‐
            cuted.
 
            Although each tuple returned by $fetch_tuple_sub is effectively
            used to call $sth->execute(@$tuple_array_ref) the exact timing may
            vary.  Drivers are free to accumulate sets of tuples to pass to the
            database server in bulk group operations for more efficient execu‐
            tion.  However, the $fetch_tuple_sub is specifically allowed to
            return the same array reference each time (which is what
            fetchrow_arrayref() usually does).
 
            For example:
 
              my $sel = $dbh1->prepare("select foo, bar from table1");
              $sel->execute;
 
              my $ins = $dbh2->prepare("insert into table2 (foo, bar) values (?,?)");
              my $fetch_tuple_sub = sub { $sel->fetchrow_arrayref };
 
              my @tuple_status;
              $rc = $ins->execute_for_fetch($fetch_tuple_sub, \@tuple_status);
              my @errors = grep { ref $_ } @tuple_status;
 
            Similarly, if you already have an array containing the data rows to
            be processed you’d use a subroutine to shift off and return each
            array ref in turn:
 
              $ins->execute_for_fetch( sub { shift @array_of_arrays }, \@tuple_status);
 
            The "execute_for_fetch" method was added in DBI 1.38.
 
        "fetchrow_arrayref"
              $ary_ref = $sth->fetchrow_arrayref;
              $ary_ref = $sth->fetch;    # alias
 
            Fetches the next row of data and returns a reference to an array
            holding the field values.  Null fields are returned as "undef" val‐
            ues in the array.  This is the fastest way to fetch data, particu‐
            larly if used with "$sth->bind_columns".
 
            If there are no more rows or if an error occurs, then
            "fetchrow_arrayref" returns an "undef". You should check
            "$sth->err" afterwards (or use the "RaiseError" attribute) to dis‐
            cover if the "undef" returned was due to an error.
 
            Note that the same array reference is returned for each fetch, so
            don’t store the reference and then use it after a later fetch.
            Also, the elements of the array are also reused for each row, so
            take care if you want to take a reference to an element. See also
            "bind_columns".
 
        "fetchrow_array"
             @ary = $sth->fetchrow_array;
 
            An alternative to "fetchrow_arrayref". Fetches the next row of data
            and returns it as a list containing the field values.  Null fields
            are returned as "undef" values in the list.
 
            If there are no more rows or if an error occurs, then
            "fetchrow_array" returns an empty list. You should check
            "$sth->err" afterwards (or use the "RaiseError" attribute) to dis‐
            cover if the empty list returned was due to an error.
 
            If called in a scalar context for a statement handle that has more
            than one column, it is undefined whether the driver will return the
            value of the first column or the last. So don’t do that.  Also, in
            a scalar context, an "undef" is returned if there are no more rows
            or if an error occurred. That "undef" can’t be distinguished from
            an "undef" returned because the first field value was NULL.  For
            these reasons you should exercise some caution if you use
            "fetchrow_array" in a scalar context.
 
        "fetchrow_hashref"
             $hash_ref = $sth->fetchrow_hashref;
             $hash_ref = $sth->fetchrow_hashref($name);
 
            An alternative to "fetchrow_arrayref". Fetches the next row of data
            and returns it as a reference to a hash containing field name and
            field value pairs.  Null fields are returned as "undef" values in
            the hash.
 
            If there are no more rows or if an error occurs, then
            "fetchrow_hashref" returns an "undef". You should check "$sth->err"
            afterwards (or use the "RaiseError" attribute) to discover if the
            "undef" returned was due to an error.
 
            The optional $name parameter specifies the name of the statement
            handle attribute. For historical reasons it defaults to ""NAME"",
            however using either ""NAME_lc"" or ""NAME_uc"" is recomended for
            portability.
 
            The keys of the hash are the same names returned by
            "$sth->{$name}". If more than one field has the same name, there
            will only be one entry in the returned hash for those fields.
 
            Because of the extra work "fetchrow_hashref" and Perl have to per‐
            form, it is not as efficient as "fetchrow_arrayref" or
            "fetchrow_array".
 
            By default a reference to a new hash is returned for each row.  It
            is likely that a future version of the DBI will support an
            attribute which will enable the same hash to be reused for each
            row. This will give a significant performance boost, but it won’t
            be enabled by default because of the risk of breaking old code.
 
        "fetchall_arrayref"
              $tbl_ary_ref = $sth->fetchall_arrayref;
              $tbl_ary_ref = $sth->fetchall_arrayref( $slice );
              $tbl_ary_ref = $sth->fetchall_arrayref( $slice, $max_rows  );
 
            The "fetchall_arrayref" method can be used to fetch all the data to
            be returned from a prepared and executed statement handle. It
            returns a reference to an array that contains one reference per
            row.
 
            If there are no rows to return, "fetchall_arrayref" returns a ref‐
            erence to an empty array. If an error occurs, "fetchall_arrayref"
            returns the data fetched thus far, which may be none.  You should
            check "$sth->err" afterwards (or use the "RaiseError" attribute) to
            discover if the data is complete or was truncated due to an error.
 
            If $slice is an array reference, "fetchall_arrayref" uses
            "fetchrow_arrayref" to fetch each row as an array ref. If the
            $slice array is not empty then it is used as a slice to select
            individual columns by perl array index number (starting at 0,
            unlike column and parameter numbers which start at 1).
 
            With no parameters, or if $slice is undefined, "fetchall_arrayref"
            acts as if passed an empty array ref.
 
            If $slice is a hash reference, "fetchall_arrayref" uses
            "fetchrow_hashref" to fetch each row as a hash reference. If the
            $slice hash is empty then fetchrow_hashref() is simply called in a
            tight loop and the keys in the hashes have whatever name lettercase
            is returned by default from fetchrow_hashref.  (See "FetchHashKey‐
            Name" attribute.) If the $slice hash is not empty, then it is used
            as a slice to select individual columns by name.  The values of the
            hash should be set to 1.  The key names of the returned hashes
            match the letter case of the names in the parameter hash, regard‐
            less of the "FetchHashKeyName" attribute.
 
            For example, to fetch just the first column of every row:
 
              $tbl_ary_ref = $sth->fetchall_arrayref([0]);
 
            To fetch the second to last and last column of every row:
 
              $tbl_ary_ref = $sth->fetchall_arrayref([-2,-1]);
 
            To fetch all fields of every row as a hash ref:
 
              $tbl_ary_ref = $sth->fetchall_arrayref({});
 
            To fetch only the fields called "foo" and "bar" of every row as a
            hash ref (with keys named "foo" and "BAR"):
 
              $tbl_ary_ref = $sth->fetchall_arrayref({ foo=>1, BAR=>1 });
 
            The first two examples return a reference to an array of array
            refs.  The third and forth return a reference to an array of hash
            refs.
 
            If $max_rows is defined and greater than or equal to zero then it
            is used to limit the number of rows fetched before returning.
            fetchall_arrayref() can then be called again to fetch more rows.
            This is especially useful when you need the better performance of
            fetchall_arrayref() but don’t have enough memory to fetch and
            return all the rows in one go. Here’s an example:
 
              my $rows = []; # cache for batches of rows
              while( my $row = ( shift(@$rows) || # get row from cache, or reload cache:
                                 shift(@{$rows=$sth->fetchall_arrayref(undef,10_000)||[]}) )
              ) {
                ...
              }
 
            That can be the fastest way to fetch and process lots of rows using
            the DBI, but it depends on the relative cost of method calls vs
            memory allocation.
 
            A standard "while" loop with column binding is often faster because
            the cost of allocating memory for the batch of rows is greater than
            the saving by reducing method calls. It’s possible that the DBI may
            provide a way to reuse the memory of a previous batch in future,
            which would then shift the balance back towards
            fetchall_arrayref().
 
        "fetchall_hashref"
              $hash_ref = $sth->fetchall_hashref($key_field);
 
            The "fetchall_hashref" method can be used to fetch all the data to
            be returned from a prepared and executed statement handle. It
            returns a reference to a hash containing a key for each distinct
            value of the $key_field column that was fetched. For each key the
            corresponding value is a reference to a hash containing all the
            selected columns and their values, as returned by
            fetchrow_hashref().
 
            If there are no rows to return, "fetchall_hashref" returns a refer‐
            ence to an empty hash. If an error occurs, "fetchall_hashref"
            returns the data fetched thus far, which may be none.  You should
            check "$sth->err" afterwards (or use the "RaiseError" attribute) to
            discover if the data is complete or was truncated due to an error.
 
            The $key_field parameter provides the name of the field that holds
            the value to be used for the key for the returned hash.  For exam‐
            ple:
 
              $dbh->{FetchHashKeyName} = ’NAME_lc’;
              $sth = $dbh->prepare("SELECT FOO, BAR, ID, NAME, BAZ FROM TABLE");
              $sth->execute;
              $hash_ref = $sth->fetchall_hashref(’id’);
              print "Name for id 42 is $hash_ref->{42}->{name}\n";
 
            The $key_field parameter can also be specified as an integer column
            number (counting from 1).  If $key_field doesn’t match any column
            in the statement, as a name first then as a number, then an error
            is returned.
 
            For queries returing more than one ’key’ column, you can specify
            multiple column names by passing $key_field as a reference to an
            array containing one or more key column names (or index numbers).
            For example:
 
              $sth = $dbh->prepare("SELECT foo, bar, baz FROM table");
              $sth->execute;
              $hash_ref = $sth->fetchall_hashref( [ qw(foo bar) ] );
              print "For foo 42 and bar 38, baz is $hash_ref->{42}->{38}->{baz}\n";
 
            The fetchall_hashref() method is normally used only where the key
            fields values for each row are unique.  If multiple rows are
            returned with the same values for the key fields then later rows
            overwrite earlier ones.
 
        "finish"
              $rc  = $sth->finish;
 
            Indicate that no more data will be fetched from this statement han‐
            dle before it is either executed again or destroyed.  The "finish"
            method is rarely needed, and frequently overused, but can sometimes
            be helpful in a few very specific situations to allow the server to
            free up resources (such as sort buffers).
 
            When all the data has been fetched from a "SELECT" statement, the
            driver should automatically call "finish" for you. So you should
            not normally need to call it explicitly except when you know that
            you’ve not fetched all the data from a statement handle.  The most
            common example is when you only want to fetch one row, but in that
            case the "selectrow_*" methods are usually better anyway.  Adding
            calls to "finish" after each fetch loop is a common mistake, don’t
            do it, it can mask genuine problems like uncaught fetch errors.
 
            Consider a query like:
 
              SELECT foo FROM table WHERE bar=? ORDER BY foo
 
            where you want to select just the first (smallest) "foo" value from
            a very large table. When executed, the database server will have to
            use temporary buffer space to store the sorted rows. If, after exe‐
            cuting the handle and selecting one row, the handle won’t be re-
            executed for some time and won’t be destroyed, the "finish" method
            can be used to tell the server that the buffer space can be freed.
 
            Calling "finish" resets the "Active" attribute for the statement.
            It may also make some statement handle attributes (such as "NAME"
            and "TYPE") unavailable if they have not already been accessed (and
            thus cached).
 
            The "finish" method does not affect the transaction status of the
            database connection.  It has nothing to do with transactions. It’s
            mostly an internal "housekeeping" method that is rarely needed.
            See also "disconnect" and the "Active" attribute.
 
            The "finish" method should have been called "discard_pending_rows".
 
        "rows"
              $rv = $sth->rows;
 
            Returns the number of rows affected by the last row affecting com‐
            mand, or -1 if the number of rows is not known or not available.
 
            Generally, you can only rely on a row count after a non-"SELECT"
            "execute" (for some specific operations like "UPDATE" and
            "DELETE"), or after fetching all the rows of a "SELECT" statement.
 
            For "SELECT" statements, it is generally not possible to know how
            many rows will be returned except by fetching them all.  Some
            drivers will return the number of rows the application has fetched
            so far, but others may return -1 until all rows have been fetched.
            So use of the "rows" method or $DBI::rows with "SELECT" statements
            is not recommended.
 
            One alternative method to get a row count for a "SELECT" is to exe‐
            cute a "SELECT COUNT(*) FROM ..." SQL statement with the same "..."
            as your query and then fetch the row count from that.
 
        "bind_col"
              $rc = $sth->bind_col($column_number, \$var_to_bind);
              $rc = $sth->bind_col($column_number, \$var_to_bind, \%attr );
              $rc = $sth->bind_col($column_number, \$var_to_bind, $bind_type );
 
            Binds a Perl variable and/or some attributes to an output column
            (field) of a "SELECT" statement.  Column numbers count up from 1.
            You do not need to bind output columns in order to fetch data.  For
            maximum portability between drivers, bind_col() should be called
            after execute() and not before.  See also "bind_columns" for an
            example.
 
            The binding is performed at a low level using Perl aliasing.  When‐
            ever a row is fetched from the database $var_to_bind appears to be
            automatically updated simply because it now refers to the same mem‐
            ory location as the corresponding column value.  This makes using
            bound variables very efficient.  Binding a tied variable doesn’t
            work, currently.
 
            The "bind_param" method performs a similar, but opposite, function
            for input variables.
 
            Data Types for Column Binding
 
            The "\%attr" parameter can be used to hint at the data type format‐
            ting the column should have. For example, you can use:
 
              $sth->bind_col(1, undef, { TYPE => SQL_DATETIME });
 
            to specify that you’d like the column (which presumably is some
            kind of datetime type) to be returned in the standard format for
            SQL_DATETIME, which is ’YYYY-MM-DD HH:MM:SS’, rather than the
            native formatting the database would normally use.
 
            There’s no $var_to_bind in that example to emphasize the point that
            bind_col() works on the underlying column value and not just a par‐
            ticular bound variable.
 
            As a short-cut for the common case, the data type can be passed
            directly, in place of the "\%attr" hash reference. This example is
            equivalent to the one above:
 
              $sth->bind_col(1, undef, SQL_DATETIME);
 
            The "TYPE" value indicates the standard (non-driver-specific) type
            for this parameter. To specify the driver-specific type, the driver
            may support a driver-specific attribute, such as "{ ora_type => 97
            }".
 
            The SQL_DATETIME and other related constants can be imported using
 
              use DBI qw(:sql_types);
 
            See "DBI Constants" for more information.
 
            The data type for a bind variable cannot be changed after the first
            "bind_col" call. In fact the whole \%attr parameter is ’sticky’ in
            the sense that a driver only needs to consider the \%attr parameter
            for the first call for a given $sth and column.
 
            The TYPE attribute for bind_col() was first specified in DBI 1.41.
 
        "bind_columns"
              $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
 
            Calls "bind_col" for each column of the "SELECT" statement.
 
            The list of references should have the same number of elements as
            the number of columns in the "SELECT" statement. If it doesn’t then
            "bind_columns" will bind the elements given, upto the number of
            columns, and then return an error.
 
            For maximum portability between drivers, bind_columns() should be
            called after execute() and not before.
 
            For example:
 
              $dbh->{RaiseError} = 1; # do this, or check every call for errors
              $sth = $dbh->prepare(q{ SELECT region, sales FROM sales_by_region });
              $sth->execute;
              my ($region, $sales);
 
              # Bind Perl variables to columns:
              $rv = $sth->bind_columns(\$region, \$sales);
 
              # you can also use Perl’s \(...) syntax (see perlref docs):
              #     $sth->bind_columns(\($region, $sales));
 
              # Column binding is the most efficient way to fetch data
              while ($sth->fetch) {
                  print "$region: $sales\n";
              }
 
            For compatibility with old scripts, the first parameter will be
            ignored if it is "undef" or a hash reference.
 
            Here’s a more fancy example that binds columns to the values inside
            a hash (thanks to H.Merijn Brand):
 
              $sth->execute;
              my %row;
              $sth->bind_columns( \( @row{ @{$sth->{NAME_lc} } } ));
              while ($sth->fetch) {
                  print "$row{region}: $row{sales}\n";
              }
 
        "dump_results"
              $rows = $sth->dump_results($maxlen, $lsep, $fsep, $fh);
 
            Fetches all the rows from $sth, calls "DBI::neat_list" for each
            row, and prints the results to $fh (defaults to "STDOUT") separated
            by $lsep (default "\n"). $fsep defaults to ", " and $maxlen
            defaults to 35.
 
            This method is designed as a handy utility for prototyping and
            testing queries. Since it uses "neat_list" to format and edit the
            string for reading by humans, it is not recomended for data trans‐
            fer applications.
 
        Statement Handle Attributes
 
        This section describes attributes specific to statement handles. Most
        of these attributes are read-only.
 
        Changes to these statement handle attributes do not affect any other
        existing or future statement handles.
 
        Attempting to set or get the value of an unknown attribute generates a
        warning, except for private driver specific attributes (which all have
        names starting with a lowercase letter).
 
        Example:
 
          ... = $h->{NUM_OF_FIELDS};    # get/read
 
        Some drivers cannot provide valid values for some or all of these
        attributes until after "$sth->execute" has been successfully called.
        Typically the attribute will be "undef" in these situations.
 
        Some attributes, like NAME, are not appropriate to some types of state‐
        ment, like SELECT. Typically the attribute will be "undef" in these
        situations.
 
        See also "finish" to learn more about the effect it may have on some
        attributes.
 
        "NUM_OF_FIELDS"  (integer, read-only)
            Number of fields (columns) in the data the prepared statement may
            return.  Statements that don’t return rows of data, like "DELETE"
            and "CREATE" set "NUM_OF_FIELDS" to 0 (though it may be undef in
            some drivers).
 
        "NUM_OF_PARAMS"  (integer, read-only)
            The number of parameters (placeholders) in the prepared statement.
            See SUBSTITUTION VARIABLES below for more details.
 
        "NAME"  (array-ref, read-only)
            Returns a reference to an array of field names for each column. The
            names may contain spaces but should not be truncated or have any
            trailing space. Note that the names have the letter case (upper,
            lower or mixed) as returned by the driver being used. Portable
            applications should use "NAME_lc" or "NAME_uc".
 
              print "First column name: $sth->{NAME}->[0]\n";
 
        "NAME_lc"  (array-ref, read-only)
            Like "NAME" but always returns lowercase names.
 
        "NAME_uc"  (array-ref, read-only)
            Like "NAME" but always returns uppercase names.
 
        "NAME_hash"  (hash-ref, read-only)
        "NAME_lc_hash"  (hash-ref, read-only)
        "NAME_uc_hash"  (hash-ref, read-only)
            The "NAME_hash", "NAME_lc_hash", and "NAME_uc_hash" attributes
            return column name information as a reference to a hash.
 
            The keys of the hash are the names of the columns.  The letter case
            of the keys corresponds to the letter case returned by the "NAME",
            "NAME_lc", and "NAME_uc" attributes respectively (as described
            above).
 
            The value of each hash entry is the perl index number of the corre‐
            sponding column (counting from 0). For example:
 
              $sth = $dbh->prepare("select Id, Name from table");
              $sth->execute;
              @row = $sth->fetchrow_array;
              print "Name $row[ $sth->{NAME_lc_hash}{name} ]\n";
 
        "TYPE"  (array-ref, read-only)
            Returns a reference to an array of integer values for each column.
            The value indicates the data type of the corresponding column.
 
            The values correspond to the international standards (ANSI X3.135
            and ISO/IEC 9075) which, in general terms, means ODBC. Driver-spe‐
            cific types that don’t exactly match standard types should gener‐
            ally return the same values as an ODBC driver supplied by the mak‐
            ers of the database. That might include private type numbers in
            ranges the vendor has officially registered with the ISO working
            group:
 
ftp://sqlstandards.org/SC32/SQL_Registry/
 
            Where there’s no vendor-supplied ODBC driver to be compatible with,
            the DBI driver can use type numbers in the range that is now offi‐
            cially reserved for use by the DBI: -9999 to -9000.
 
            All possible values for "TYPE" should have at least one entry in
            the output of the "type_info_all" method (see "type_info_all").
 
        "PRECISION"  (array-ref, read-only)
            Returns a reference to an array of integer values for each column.
 
            For numeric columns, the value is the maximum number of digits
            (without considering a sign character or decimal point). Note that
            the "display size" for floating point types (REAL, FLOAT, DOUBLE)
            can be up to 7 characters greater than the precision (for the sign
            + decimal point + the letter E + a sign + 2 or 3 digits).
 
            For any character type column the value is the OCTET_LENGTH, in
            other words the number of bytes, not characters.
 
            (More recent standards refer to this as COLUMN_SIZE but we stick
            with PRECISION for backwards compatibility.)
 
        "SCALE"  (array-ref, read-only)
            Returns a reference to an array of integer values for each column.
            NULL ("undef") values indicate columns where scale is not applica‐
            ble.
 
        "NULLABLE"  (array-ref, read-only)
            Returns a reference to an array indicating the possibility of each
            column returning a null.  Possible values are 0 (or an empty
            string) = no, 1 = yes, 2 = unknown.
 
              print "First column may return NULL\n" if $sth->{NULLABLE}->[0];
 
        "CursorName"  (string, read-only)
            Returns the name of the cursor associated with the statement han‐
            dle, if available. If not available or if the database driver does
            not support the "where current of ..." SQL syntax, then it returns
            "undef".
 
        "Database"  (dbh, read-only)
            Returns the parent $dbh of the statement handle.
 
        "ParamValues"  (hash ref, read-only)
            Returns a reference to a hash containing the values currently bound
            to placeholders.  The keys of the hash are the ’names’ of the
            placeholders, typically integers starting at 1.  Returns undef if
            not supported by the driver.
 
            See "ShowErrorStatement" for an example of how this is used.
 
            If the driver supports "ParamValues" but no values have been bound
            yet then the driver should return a hash with placeholders names in
            the keys but all the values undef, but some drivers may return a
            ref to an empty hash.
 
            It is possible that the values in the hash returned by "ParamVal‐
            ues" are not exactly the same as those passed to bind_param() or
            execute().  The driver may have slightly modified values in some
            way based on the TYPE the value was bound with. For example a
            floating point value bound as an SQL_INTEGER type may be returned
            as an integer.  The values returned by "ParamValues" can be passed
            to another bind_param() method with the same TYPE and will be seen
            by the database as the same value.
 
            It is also possible that the keys in the hash returned by "Param‐
            Values" are not exactly the same as those implied by the prepared
            statement.  For example, DBD::Oracle translates ’"?"’ placeholders
            into ’":pN"’ where N is a sequence number starting at 1.
 
            The "ParamValues" attribute was added in DBI 1.28.
 
        "ParamArrays"  (hash ref, read-only)
            Returns a reference to a hash containing the values currently bound
            to placeholders with "execute_array" or "bind_param_array".  The
            keys of the hash are the ’names’ of the placeholders, typically
            integers starting at 1.  Returns undef if not supported by the
            driver or no arrays of parameters are bound.
 
            Each key value is an array reference containing a list of the bound
            parameters for that column.
 
            For example:
 
              $sth = $dbh->prepare("INSERT INTO staff (id, name) values (?,?)");
              $sth->execute_array({},[1,2], [’fred’,’dave’]);
              if ($sth->{ParamArrays}) {
                  foreach $param (keys %{$sth->{ParamArrays}}) {
                      printf "Parameters for %s : %s\n", $param,
                      join(",", @{$sth->{ParamArrays}->{$param}});
                  }
              }
 
            It is possible that the values in the hash returned by "ParamAr‐
            rays" are not exactly the same as those passed to
            "bind_param_array" or "execute_array".  The driver may have
            slightly modified values in some way based on the TYPE the value
            was bound with. For example a floating point value bound as an
            SQL_INTEGER type may be returned as an integer.
 
            It is also possible that the keys in the hash returned by "ParamAr‐
            rays" are not exactly the same as those implied by the prepared
            statement.  For example, DBD::Oracle translates ’"?"’  placeholders
            into ’":pN"’ where N is a sequence number starting at 1.
 
        "ParamTypes"  (hash ref, read-only)
            Returns a reference to a hash containing the type information cur‐
            rently bound to placeholders.  The keys of the hash are the ’names’
            of the placeholders: either integers starting at 1, or, for drivers
            that support named placeholders, the actual parameter name string.
            The hash values are hashrefs of type information in the same form
            as that provided to the various bind_param() methods (See "Data
            Types for Placeholders" for the format and values), plus anything
            else that was passed as the third argument to bind_param().
            Returns undef if not supported by the driver.
 
            If the driver supports "ParamTypes", but no values have been bound
            yet, then the driver should return a hash with the placeholder name
            keys, but all the values undef; however, some drivers may return a
            ref to an empty hash, or, alternately, may provide type information
            supplied by the database (only a few databases can do that).
 
            It is possible that the values in the hash returned by "ParamTypes"
            are not exactly the same as those passed to bind_param() or exe‐
            cute().  The driver may have modified the type information in some
            way based on the bound values, other hints provided by the pre‐
            pare()’d SQL statement, or alternate type mappings required by the
            driver or target database system.
 
            It is also possible that the keys in the hash returned by "Param‐
            Types" are not exactly the same as those implied by the prepared
            statement.  For example, DBD::Oracle translates ’"?"’ placeholders
            into ’":pN"’ where N is a sequence number starting at 1.
 
            The "ParamTypes" attribute was added in DBI 1.49. Implementation is
            the responsibility of individual drivers; the DBI layer default
            implementation simply returns undef.
 
        "Statement"  (string, read-only)
            Returns the statement string passed to the "prepare" method.
 
        "RowsInCache"  (integer, read-only)
            If the driver supports a local row cache for "SELECT" statements,
            then this attribute holds the number of un-fetched rows in the
            cache. If the driver doesn’t, then it returns "undef". Note that
            some drivers pre-fetch rows on execute, whereas others wait till
            the first fetch.
 
            See also the "RowCacheSize" database handle attribute.
        "install_method"
                DBD::Foo::db->install_method($method_name, \%attr);
 
            Installs the driver-private method named by $method_name into the
            DBI method dispatcher so it can be called directly, avoiding the
            need to use the func() method.
 
            It is called as a static method on the driver class to which the
            method belongs. The method name must begin with the corresponding
            registered driver-private prefix. For example, for DBD::Oracle
            $method_name must being with ’"ora_"’, and for DBD::AnyData it must
            begin with ’"ad_"’.
 
            The attributes can be used to provide fine control over how the DBI
            dispatcher handles the dispatching of the method. However, at this
            point, it’s undocumented and very liable to change. (Volunteers to
            polish up and document the interface are very welcome to get in
            touch via dbi-dev@perl.org)
 
            Methods installed using install_method default to the standard
            error handling behaviour for DBI methods: clearing err and errstr
            before calling the method, and checking for errors to trigger
            RaiseError etc. on return. This differs from the default behaviour
            of func().
 
            Note for driver authors: The DBD::Foo::xx->install_method call
            won’t work until the class-hierarchy has been setup. Normally the
            DBI looks after that just after the driver is loaded. This means
            install_method() can’t be called at the time the driver is loaded
            unless the class-hierarchy is set up first. The way to do that is
            to call the setup_driver() method:
 
                DBI->setup_driver(’DBD::Foo’);
 
            before using install_method().
        Catalog Methods
 
        An application can retrieve metadata information from the DBMS by issu‐
        ing appropriate queries on the views of the Information Schema. Unfor‐
        tunately, "INFORMATION_SCHEMA" views are seldom supported by the DBMS.
        Special methods (catalog methods) are available to return result sets
        for a small but important portion of that metadata:
 
          column_info
          foreign_key_info
          primary_key_info
          table_info
          statistics_info
 
        All catalog methods accept arguments in order to restrict the result
        sets.  Passing "undef" to an optional argument does not constrain the
        search for that argument.  However, an empty string (’’) is treated as
        a regular search criteria and will only match an empty value.
 
        Note: SQL/CLI and ODBC differ in the handling of empty strings. An
        empty string will not restrict the result set in SQL/CLI.
 
        Most arguments in the catalog methods accept only ordinary values, e.g.
        the arguments of "primary_key_info()".  Such arguments are treated as a
        literal string, i.e. the case is significant and quote characters are
        taken literally.
 
        Some arguments in the catalog methods accept search patterns (strings
        containing ’_’ and/or ’%’), e.g. the $table argument of "col‐
        umn_info()".  Passing ’%’ is equivalent to leaving the argument
        "undef".
 
        Caveat: The underscore (’_’) is valid and often used in SQL identi‐
        fiers.  Passing such a value to a search pattern argument may return
        more rows than expected!  To include pattern characters as literals,
        they must be preceded by an escape character which can be achieved with
 
          $esc = $dbh->get_info( 14 );  # SQL_SEARCH_PATTERN_ESCAPE
          $search_pattern =~ s/([_%])/$esc$1/g;
 
        The ODBC and SQL/CLI specifications define a way to change the default
        behaviour described above: All arguments (except list value arguments)
        are treated as identifier if the "SQL_ATTR_METADATA_ID" attribute is
        set to "SQL_TRUE".  Quoted identifiers are very similar to ordinary
        values, i.e. their body (the string within the quotes) is interpreted
        literally.  Unquoted identifiers are compared in UPPERCASE.
 
        The DBI (currently) does not support the "SQL_ATTR_METADATA_ID"
        attribute, i.e. it behaves like an ODBC driver where "SQL_ATTR_META‐
        DATA_ID" is set to "SQL_FALSE".
 
        Transactions
 
        Transactions are a fundamental part of any robust database system. They
        protect against errors and database corruption by ensuring that sets of
        related changes to the database take place in atomic (indivisible,
        all-or-nothing) units.
 
        This section applies to databases that support transactions and where
        "AutoCommit" is off.  See "AutoCommit" for details of using "AutoCom‐
        mit" with various types of databases.
 
        The recommended way to implement robust transactions in Perl applica‐
        tions is to use "RaiseError" and "eval { ... }" (which is very fast,
        unlike "eval "...""). For example:
 
          $dbh->{AutoCommit} = 0;  # enable transactions, if possible
          $dbh->{RaiseError} = 1;
          eval {
              foo(...)        # do lots of work here
              bar(...)        # including inserts
              baz(...)        # and updates
              $dbh->commit;   # commit the changes if we get this far
          };
          if ($@) {
              warn "Transaction aborted because $@";
              # now rollback to undo the incomplete changes
              # but do it in an eval{} as it may also fail
              eval { $dbh->rollback };
              # add other application on-error-clean-up code here
          }
 
        If the "RaiseError" attribute is not set, then DBI calls would need to
        be manually checked for errors, typically like this:
 
          $h->method(@args) or die $h->errstr;
 
        With "RaiseError" set, the DBI will automatically "die" if any DBI
        method call on that handle (or a child handle) fails, so you don’t have
        to test the return value of each method call. See "RaiseError" for more
        details.
 
        A major advantage of the "eval" approach is that the transaction will
        be properly rolled back if any code (not just DBI calls) in the inner
        application dies for any reason. The major advantage of using the
        "$h->{RaiseError}" attribute is that all DBI calls will be checked
        automatically. Both techniques are strongly recommended.
 
        After calling "commit" or "rollback" many drivers will not let you
        fetch from a previously active "SELECT" statement handle that’s a child
        of the same database handle. A typical way round this is to connect the
        the database twice and use one connection for "SELECT" statements.
 
        See "AutoCommit" and "disconnect" for other important information about
        transactions.
 
        Handling BLOB / LONG / Memo Fields
 
        Many databases support "blob" (binary large objects), "long", or simi‐
        lar datatypes for holding very long strings or large amounts of binary
        data in a single field. Some databases support variable length long
        values over 2,000,000,000 bytes in length.
 
        Since values of that size can’t usually be held in memory, and because
        databases can’t usually know in advance the length of the longest long
        that will be returned from a "SELECT" statement (unlike other data
        types), some special handling is required.
 
        In this situation, the value of the "$h->{LongReadLen}" attribute is
        used to determine how much buffer space to allocate when fetching such
        fields.  The "$h->{LongTruncOk}" attribute is used to determine how to
        behave if a fetched value can’t fit into the buffer.
 
        See the description of "LongReadLen" for more information.
 
        When trying to insert long or binary values, placeholders should be
        used since there are often limits on the maximum size of an "INSERT"
        statement and the "quote" method generally can’t cope with binary data.
        See "Placeholders and Bind Values".
 
        Simple Examples
 
        Here’s a complete example program to select and fetch some data:
 
          my $data_source = "dbi::DriverName:db_name";
          my $dbh = DBI->connect($data_source, $user, $password)
              or die "Can’t connect to $data_source: $DBI::errstr";
 
          my $sth = $dbh->prepare( q{
                  SELECT name, phone
                  FROM mytelbook
          }) or die "Can’t prepare statement: $DBI::errstr";
 
          my $rc = $sth->execute
              or die "Can’t execute statement: $DBI::errstr";
 
          print "Query will return $sth->{NUM_OF_FIELDS} fields.\n\n";
          print "Field names: @{ $sth->{NAME} }\n";
 
          while (($name, $phone) = $sth->fetchrow_array) {
              print "$name: $phone\n";
          }
          # check for problems which may have terminated the fetch early
          die $sth->errstr if $sth->err;
 
          $dbh->disconnect;
 
        Here’s a complete example program to insert some data from a file.
        (This example uses "RaiseError" to avoid needing to check each call).
 
          my $dbh = DBI->connect("dbi:DriverName:db_name", $user, $password, {
              RaiseError => 1, AutoCommit => 0
          });
 
          my $sth = $dbh->prepare( q{
              INSERT INTO table (name, phone) VALUES (?, ?)
          });
 
          open FH, "<phone.csv" or die "Unable to open phone.csv: $!";
          while (<FH>) {
              chomp;
              my ($name, $phone) = split /,/;
              $sth->execute($name, $phone);
          }
          close FH;
 
          $dbh->commit;
          $dbh->disconnect;
 
        Here’s how to convert fetched NULLs (undefined values) into empty
        strings:
 
          while($row = $sth->fetchrow_arrayref) {
            # this is a fast and simple way to deal with nulls:
            foreach (@$row) { $_ = ’’ unless defined }
            print "@$row\n";
          }
 
        The "q{...}" style quoting used in these examples avoids clashing with
        quotes that may be used in the SQL statement. Use the double-quote like
        "qq{...}" operator if you want to interpolate variables into the
        string.  See "Quote and Quote-like Operators" in perlop for more
        details.
 
        Threads and Thread Safety
 
        Perl 5.7 and later support a new threading model called iThreads.  (The
        old "5.005 style" threads are not supported by the DBI.)
 
        In the iThreads model each thread has it’s own copy of the perl inter‐
        preter.  When a new thread is created the original perl interpreter is
        ’cloned’ to create a new copy for the new thread.
 
        If the DBI and drivers are loaded and handles created before the thread
        is created then it will get a cloned copy of the DBI, the drivers and
        the handles.
 
        However, the internal pointer data within the handles will refer to the
        DBI and drivers in the original interpreter. Using those handles in the
        new interpreter thread is not safe, so the DBI detects this and croaks
        on any method call using handles that don’t belong to the current
        thread (except for DESTROY).
 
        Because of this (possibly temporary) restriction, newly created threads
        must make their own connctions to the database. Handles can’t be shared
        across threads.
 
        But BEWARE, some underlying database APIs (the code the DBD driver uses
        to talk to the database, often supplied by the database vendor) are not
        thread safe. If it’s not thread safe, then allowing more than one
        thread to enter the code at the same time may cause subtle/serious
        problems. In some cases allowing more than one thread to enter the
        code, even if not at the same time, can cause problems. You have been
        warned.
 
        Using DBI with perl threads is not yet recommended for production envi‐
        ronments. For more information see <http://www.perl‐
        monks.org/index.pl?node_id=288022>
 
        Note: There is a bug in perl 5.8.2 when configured with threads and
        debugging enabled (bug #24463) which causes a DBI test to fail.
 
        Signal Handling and Canceling Operations
 
        [The following only applies to systems with unix-like signal handling.
        I’d welcome additions for other systems, especially Windows.]
 
        The first thing to say is that signal handling in Perl versions less
        than 5.8 is not safe. There is always a small risk of Perl crashing
        and/or core dumping when, or after, handling a signal because the sig‐
        nal could arrive and be handled while internal data structures are
        being changed. If the signal handling code used those same internal
        data structures it could cause all manner of subtle and not-so-subtle
        problems.  The risk was reduced with 5.4.4 but was still present in all
        perls up through 5.8.0.
 
        Beginning in perl 5.8.0 perl implements ’safe’ signal handling if your
        system has the POSIX sigaction() routine. Now when a signal is deliv‐
        ered perl just makes a note of it but does not run the %SIG handler.
        The handling is ’defered’ until a ’safe’ moment.
 
        Although this change made signal handling safe, it also lead to a prob‐
        lem with signals being defered for longer than you’d like.  If a signal
        arrived while executing a system call, such as waiting for data on a
        network connection, the signal is noted and then the system call that
        was executing returns with an EINTR error code to indicate that it was
        interrupted. All fine so far.
 
        The problem comes when the code that made the system call sees the
        EINTR code and decides it’s going to call it again. Perl doesn’t do
        that, but database code sometimes does. If that happens then the signal
        handler doesn’t get called untill later. Maybe much later.
 
        Fortunately there are ways around this which we’ll discuss below.
        Unfortunately they make signals unsafe again.
 
        The two most common uses of signals in relation to the DBI are for can‐
        celing operations when the user types Ctrl-C (interrupt), and for
        implementing a timeout using "alarm()" and $SIG{ALRM}.
 
        Cancel
            The DBI provides a "cancel" method for statement handles. The "can‐
            cel" method should abort the current operation and is designed to
            be called from a signal handler.  For example:
 
              $SIG{INT} = sub { $sth->cancel };
 
            However, few drivers implement this (the DBI provides a default
            method that just returns "undef") and, even if implemented, there
            is still a possibility that the statement handle, and even the par‐
            ent database handle, will not be usable afterwards.
 
            If "cancel" returns true, then it has successfully invoked the
            database engine’s own cancel function.  If it returns false, then
            "cancel" failed. If it returns "undef", then the database driver
            does not have cancel implemented.
 
        Timeout
            The traditional way to implement a timeout is to set $SIG{ALRM} to
            refer to some code that will be executed when an ALRM signal
            arrives and then to call alarm($seconds) to schedule an ALRM signal
            to be delivered $seconds in the future. For example:
 
              eval {
                local $SIG{ALRM} = sub { die "TIMEOUT\n" };
                alarm($seconds);
                ... code to execute with timeout here ...
                alarm(0);  # cancel alarm (if code ran fast)
              };
              alarm(0);    # cancel alarm (if eval failed)
              if ( $@ eq "TIMEOUT" ) { ... }
 
            Unfortunately, as described above, this won’t always work as
            expected, depending on your perl version and the underlying
            database code.
 
            With Oracle for instance (DBD::Oracle), if the system which hosts
            the database is down the DBI->connect() call will hang for several
            minutes before returning an error.
 
        The solution on these systems is to use the "POSIX::sigaction()" rou‐
        tine to gain low level access to how the signal handler is installed.
 
        The code would look something like this (for the DBD-Oracle connect()):
 
           use POSIX ’:signal_h’;
 
           my $mask = POSIX::SigSet->new( SIGALRM ); # signals to mask in the handler
           my $action = POSIX::SigAction->new(
               sub { die "connect timeout" },        # the handler code ref
               $mask,
               # not using (perl 5.8.2 and later) ’safe’ switch or sa_flags
           );
           my $oldaction = POSIX::SigAction->new();
           sigaction( ’ALRM’, $action, $oldaction );
           my $dbh;
           eval {
alarm(5); # seconds before time out
              $dbh = DBI->connect("dbi:Oracle:$dsn" ... );
              alarm(0); # cancel alarm (if connect worked fast)
           };
           alarm(0);    # cancel alarm (if eval failed)
           sigaction( ’ALRM’, $oldaction );  # restore original signal handler
           if ( $@ ) ....
 
        Similar techniques can be used for canceling statement execution.
 
        Unfortunately, this solution is somewhat messy, and it does not work
        with perl versions less than perl 5.8 where "POSIX::sigaction()"
        appears to be broken.
 
        For a cleaner implementation that works across perl versions, see Lin‐
        coln Baxter’s Sys::SigAction module at <http://search.cpan.org/~lbax‐
        ter/Sys-SigAction/>.  The documentation for Sys::SigAction includes an
        longer discussion of this problem, and a DBD::Oracle test script.
 
        Be sure to read all the signal handling sections of the perlipc manual.
 
        And finally, two more points to keep firmly in mind. Firstly, remember
        that what we’ve done here is essentially revert to old style unsafe
        handling of these signals. So do as little as possible in the handler.
        Ideally just die(). Secondly, the handles in use at the time the signal
        is handled may not be safe to use afterwards.
 
        Subclassing the DBI
 
        DBI can be subclassed and extended just like any other object oriented
        module.  Before we talk about how to do that, it’s important to be
        clear about the various DBI classes and how they work together.
 
        By default "$dbh = DBI->connect(...)" returns a $dbh blessed into the
        "DBI::db" class.  And the "$dbh->prepare" method returns an $sth
        blessed into the "DBI::st" class (actually it simply changes the last
        four characters of the calling handle class to be "::st").
 
        The leading ’"DBI"’ is known as the ’root class’ and the extra ’"::db"’
        or ’"::st"’ are the ’handle type suffixes’. If you want to subclass the
        DBI you’ll need to put your overriding methods into the appropriate
        classes.  For example, if you want to use a root class of "MySubDBI"
        and override the do(), prepare() and execute() methods, then your do()
        and prepare() methods should be in the "MySubDBI::db" class and the
        execute() method should be in the "MySubDBI::st" class.
 
        To setup the inheritance hierarchy the @ISA variable in "MySubDBI::db"
        should include "DBI::db" and the @ISA variable in "MySubDBI::st" should
        include "DBI::st".  The "MySubDBI" root class itself isn’t currently
        used for anything visible and so, apart from setting @ISA to include
        "DBI", it can be left empty.
 
        So, having put your overriding methods into the right classes, and
        setup the inheritance hierarchy, how do you get the DBI to use them?
        You have two choices, either a static method call using the name of
        your subclass:
 
          $dbh = MySubDBI->connect(...);
 
        or specifying a "RootClass" attribute:
 
          $dbh = DBI->connect(..., { RootClass => ’MySubDBI’ });
 
        If both forms are used then the attribute takes precedence.
 
        The only differences between the two are that using an explicit Root‐
        Class attribute will a) make the DBI automatically attempt to load a
        module by that name if the class doesn’t exist, and b) won’t call your
        MySubDBI::connect() method, if you have one.
 
        When subclassing is being used then, after a successful new connect,
        the DBI->connect method automatically calls:
 
          $dbh->connected($dsn, $user, $pass, \%attr);
 
        The default method does nothing. The call is made just to simplify any
        post-connection setup that your subclass may want to perform.  The
        parameters are the same as passed to DBI->connect.  If your subclass
        supplies a connected method, it should be part of the MySubDBI::db
        package.
 
        One more thing to note: you must let the DBI do the handle creation.
        If you want to override the connect() method in your *::dr class then
        it must still call SUPER::connect to get a $dbh to work with. Simi‐
        larly, an overridden prepare() method in *::db must still call
        SUPER::prepare to get a $sth.  If you try to create your own handles
        using bless() then you’ll find the DBI will reject them with an "is not
        a DBI handle (has no magic)" error.
 
        Here’s a brief example of a DBI subclass.  A more thorough example can
        be found in t/subclass.t in the DBI distribution.
 
          package MySubDBI;
 
          use strict;
 
          use DBI;
          use vars qw(@ISA);
          @ISA = qw(DBI);
 
          package MySubDBI::db;
          use vars qw(@ISA);
          @ISA = qw(DBI::db);
 
          sub prepare {
            my ($dbh, @args) = @_;
            my $sth = $dbh->SUPER::prepare(@args)
                or return;
            $sth->{private_mysubdbi_info} = { foo => ’bar’ };
            return $sth;
          }
 
          package MySubDBI::st;
          use vars qw(@ISA);
          @ISA = qw(DBI::st);
 
          sub fetch {
            my ($sth, @args) = @_;
            my $row = $sth->SUPER::fetch(@args)
                or return;
            do_something_magical_with_row_data($row)
                or return $sth->set_err(1234, "The magic failed", undef, "fetch");
            return $row;
          }
 
        When calling a SUPER::method that returns a handle, be careful to check
        the return value before trying to do other things with it in your over‐
        ridden method. This is especially important if you want to set a hash
        attribute on the handle, as Perl’s autovivification will bite you by
        (in)conveniently creating an unblessed hashref, which your method will
        then return with usually baffling results later on like the error
        "dbih_getcom handle HASH(0xa4451a8) is not a DBI handle (has no magic".
        It’s best to check right after the call and return undef immediately on
        error, just like DBI would and just like the example above.
 
        If your method needs to record an error it should call the set_err()
        method with the error code and error string, as shown in the example
        above. The error code and error string will be recorded in the handle
        and available via "$h->err" and $DBI::errstr etc.  The set_err() method
        always returns an undef or empty list as approriate. Since your method
        should nearly always return an undef or empty list as soon as an error
        is detected it’s handy to simply return what set_err() returns, as
        shown in the example above.
 
        If the handle has "RaiseError", "PrintError", or "HandleError" etc. set
        then the set_err() method will honour them. This means that if
        "RaiseError" is set then set_err() won’t return in the normal way but
        will ’throw an exception’ that can be caught with an "eval" block.
 
        You can stash private data into DBI handles via "$h->{private_..._*}".
        See the entry under "ATTRIBUTES COMMON TO ALL HANDLES" for info and
        important caveats.
 

TRACING

        The DBI has a powerful tracing mechanism built in. It enables you to
        see what’s going on ’behind the scenes’, both within the DBI and the
        drivers you’re using.
 
        Trace Settings
 
        Which details are written to the trace output is controlled by a combi‐
        nation of a trace level, an integer from 0 to 15, and a set of trace
        flags that are either on or off. Together these are known as the trace
        settings and are stored together in a single integer.  For normal use
        you only need to set the trace level, and generally only to a value
        between 1 and 4.
 
        Each handle has it’s own trace settings, and so does the DBI.  When you
        call a method the DBI merges the handles settings into its own for the
        duration of the call: the trace flags of the handle are OR’d into the
        trace flags of the DBI, and if the handle has a higher trace level then
        the DBI trace level is raised to match it.  The previous DBI trace set‐
        ings are restored when the called method returns.
 
        Trace Levels
 
        Trace levels are as follows:
 
          0 - Trace disabled.
          1 - Trace DBI method calls returning with results or errors.
          2 - Trace method entry with parameters and returning with results.
          3 - As above, adding some high-level information from the driver
              and some internal information from the DBI.
          4 - As above, adding more detailed information from the driver.
          5 to 15 - As above but with more and more obscure information.
 
        Trace level 1 is best for a simple overview of what’s happening.  Trace
        level 2 is a good choice for general purpose tracing.  Levels 3 and
        above are best reserved for investigating a specific problem, when you
        need to see "inside" the driver and DBI.
 
        The trace output is detailed and typically very useful. Much of the
        trace output is formatted using the "neat" function, so strings in the
        trace output may be edited and truncated by that function.
 
        Trace Flags
 
        Trace flags are used to enable tracing of specific activities within
        the DBI and drivers. The DBI defines some trace flags and drivers can
        define others. DBI trace flag names begin with a capital letter and
        driver specific names begin with a lowercase letter, as usual.
 
        Curently the DBI only defines two trace flags:
 
          ALL - turn on all DBI and driver flags (not recommended)
          SQL - trace SQL statements executed (not yet implemented)
 
        The "parse_trace_flags" and "parse_trace_flag" methods are used to con‐
        vert trace flag names into the coresponding integer bit flags.
 
        Enabling Trace
 
        The "$h->trace" method sets the trace settings for a handle and
        "DBI->trace" does the same for the DBI.
 
        In addition to the "trace" method, you can enable the same trace infor‐
        mation, and direct the output to a file, by setting the "DBI_TRACE"
        environment variable before starting Perl.  See "DBI_TRACE" for more
        information.
 
        Finally, you can set, or get, the trace settings for a handle using the
        "TraceLevel" attribute.
 
        All of those methods use parse_trace_flags() and so allow you set both
        the trace level and multiple trace flags by using a string containing
        the trace level and/or flag names separated by vertical bar (""|"") or
        comma ("","") characters. For example:
 
          local $h->{TraceLevel} = "3|SQL|foo";
 
        Trace Output
 
        Initially trace output is written to "STDERR".  Both the "$h->trace"
        and "DBI->trace" methods take an optional $trace_filename parameter. If
        specified, and can be opened in append mode, then all trace output
        (currently including that from other handles) is redirected to that
        file.  A warning is generated if the file can’t be opened.
 
        Further calls to trace() without a $trace_filename do not alter where
        the trace output is sent. If $trace_filename is undefined, then trace
        output is sent to "STDERR" and the previous trace file is closed.
 
        Currently $trace_filename can’t be a filehandle. But meanwhile you can
        use the special strings "STDERR" and "STDOUT" to select those filehan‐
        dles.
 
        Trace Content
 
        Many of the values embeded in trace output are formatted using the
        neat() utility function. This means they may be quoted, sanitized, and
        possibly truncated if longer than $DBI::neat_maxlen. See "neat" for
        more details.
 
        Tracing Tips
 
        You can add tracing to your own application code using the "trace_msg"
        method.
 
        It can sometimes be handy to compare trace files from two different
        runs of the same script. However using a tool like "diff" doesn’t work
        well because the trace file is full of object addresses that may differ
        each run. Here’s a handy little command to strip those out:
 
          perl -pe ’s/\b0x[\da-f]{6,}/0xNNNN/gi; s/\b[\da-f]{6,}/<long number>/gi’
        The DBI module recognizes a number of environment variables, but most
        of them should not be used most of the time.  It is better to be
        explicit about what you are doing to avoid the need for environment
        variables, especially in a web serving system where web servers are
        stingy about which environment variables are available.
 
        DBI_DSN
 
        The DBI_DSN environment variable is used by DBI->connect if you do not
        specify a data source when you issue the connect.  It should have a
        format such as "dbi:Driver:databasename".
 
        DBI_DRIVER
 
        The DBI_DRIVER environment variable is used to fill in the database
        driver name in DBI->connect if the data source string starts "dbi::"
        (thereby omitting the driver).  If DBI_DSN omits the driver name,
        DBI_DRIVER can fill the gap.
 
        DBI_AUTOPROXY
 
        The DBI_AUTOPROXY environment variable takes a string value that starts
        "dbi:Proxy:" and is typically followed by "hostname=...;port=...".  It
        is used to alter the behaviour of DBI->connect.  For full details, see
        DBI::Proxy documentation.
 
        DBI_USER
 
        The DBI_USER environment variable takes a string value that is used as
        the user name if the DBI->connect call is given undef (as distinct from
        an empty string) as the username argument.  Be wary of the security
        implications of using this.
 
        DBI_PASS
 
        The DBI_PASS environment variable takes a string value that is used as
        the password if the DBI->connect call is given undef (as distinct from
        an empty string) as the password argument.  Be extra wary of the secu‐
        rity implications of using this.
 
        DBI_DBNAME (obsolete)
 
        The DBI_DBNAME environment variable takes a string value that is used
        only when the obsolescent style of DBI->connect (with driver name as
        fourth parameter) is used, and when no value is provided for the first
        (database name) argument.
 
        DBI_TRACE
 
        The DBI_TRACE environment variable specifies the global default trace
        settings for the DBI at startup. Can also be used to direct trace out‐
        put to a file. When the DBI is loaded it does:
 
          DBI->trace(split /=/, $ENV{DBI_TRACE}, 2) if $ENV{DBI_TRACE};
 
        So if "DBI_TRACE" contains an ""="" character then what follows it is
        used as the name of the file to append the trace to.
 
        output appended to that file. If the name begins with a number followed
        by an equal sign ("="), then the number and the equal sign are stripped
        off from the name, and the number is used to set the trace level. For
        example:
 
          DBI_TRACE=1=dbitrace.log perl your_test_script.pl
 
        On Unix-like systems using a Bourne-like shell, you can do this easily
        on the command line:
 
          DBI_TRACE=2 perl your_test_script.pl
 
        See "TRACING" for more information.
 
        PERL_DBI_DEBUG (obsolete)
 
        An old variable that should no longer be used; equivalent to DBI_TRACE.
 
        DBI_PROFILE
 
        The DBI_PROFILE environment variable can be used to enable profiling of
        DBI method calls. See DBI::Profile for more information.
 
        DBI_PUREPERL
 
        The DBI_PUREPERL environment variable can be used to enable the use of
        DBI::PurePerl.  See DBI::PurePerl for more information.
        Fatal Errors
 
        Can’t call method "prepare" without a package or object reference
            The $dbh handle you’re using to call "prepare" is probably unde‐
            fined because the preceding "connect" failed. You should always
            check the return status of DBI methods, or use the "RaiseError"
            attribute.
 
        Can’t call method "execute" without a package or object reference
            The $sth handle you’re using to call "execute" is probably unde‐
            fined because the preceeding "prepare" failed. You should always
            check the return status of DBI methods, or use the "RaiseError"
            attribute.
 
        DBI/DBD internal version mismatch
            The DBD driver module was built with a different version of DBI
            than the one currently being used.  You should rebuild the DBD mod‐
            ule under the current version of DBI.
 
            (Some rare platforms require "static linking". On those platforms,
            there may be an old DBI or DBD driver version actually embedded in
            the Perl executable being used.)
 
        DBD driver has not implemented the AutoCommit attribute
            The DBD driver implementation is incomplete. Consult the author.
 
        Can’t [sg]et %s->{%s}: unrecognised attribute
            You attempted to set or get an unknown attribute of a handle.  Make
            sure you have spelled the attribute name correctly; case is signif‐
            icant (e.g., "Autocommit" is not the same as "AutoCommit").
        A pure-perl emulation of the DBI is included in the distribution for
        people using pure-perl drivers who, for whatever reason, can’t install
        the compiled DBI. See DBI::PurePerl.
        Driver and Database Documentation
 
        Refer to the documentation for the DBD driver that you are using.
 
        Refer to the SQL Language Reference Manual for the database engine that
        you are using.
 
        ODBC and SQL/CLI Standards Reference Information
 
        More detailed information about the semantics of certain DBI methods
        that are based on ODBC and SQL/CLI standards is available on-line via
        microsoft.com, for ODBC, and www.jtc1sc32.org for the SQL/CLI standard:
 
         DBI method        ODBC function     SQL/CLI Working Draft
         ----------        -------------     ---------------------
         column_info       SQLColumns        Page 124
         foreign_key_info  SQLForeignKeys    Page 163
         get_info          SQLGetInfo        Page 214
         primary_key_info  SQLPrimaryKeys    Page 254
         table_info        SQLTables         Page 294
         type_info         SQLGetTypeInfo    Page 239
         statistics_info   SQLStatistics
 
        For example, for ODBC information on SQLColumns you’d visit:
 
http://msdn.microsoft.com/library/en-us/odbc/htm/odbcsqlcolumns.asp
 
        If that URL ceases to work then use the MSDN search facility at:
 
http://search.microsoft.com/us/dev/
 
        and search for "SQLColumns returns" using the exact phrase option.  The
        link you want will probably just be called "SQLColumns" and will be
        part of the Data Access SDK.
 
        And for SQL/CLI standard information on SQLColumns you’d read page 124
        of the (very large) SQL/CLI Working Draft available from:
 
http://jtc1sc32.org/doc/N0701-0750/32N0744T.pdf
 
        Standards Reference Information
 
        A hyperlinked, browsable version of the BNF syntax for SQL92 (plus Ora‐
        cle 7 SQL and PL/SQL) is available here:
 
http://cui.unige.ch/db-research/Enseignement/analyseinfo/SQL92/BNFindex.html
 
        A BNF syntax for SQL3 is available here:
 
http://www.sqlstandards.org/SC32/WG3/Progression_Documents/Informal_working_drafts/iso-9075-2-1999.bnf
 
        The following links provide further useful information about SQL.  Some
        of these are rather dated now but may still be useful.
 
http://www.jcc.com/SQLPages/jccs_sql.htm
http://www.contrib.andrew.cmu.edu/~shadow/sql.html
http://www.altavista.com/query?q=sql+tutorial
 
        Books and Articles
 
        Programming the Perl DBI, by Alligator Descartes and Tim Bunce.
        <http://books.perl.org/book/154>
 
        Programming Perl 3rd Ed. by Larry Wall, Tom Christiansen & Jon Orwant.
        <http://books.perl.org/book/134>
 
        Learning Perl by Randal Schwartz.  <http://books.perl.org/book/101>
 
        Details of many other books related to perl can be found at
        <http://books.perl.org>
 
        Perl Modules
 
        Index of DBI related modules available from CPAN:
 
http://search.cpan.org/search?mode=module&query=DBIx%3A%3A
http://search.cpan.org/search?mode=doc&query=DBI
 
        For a good comparison of RDBMS-OO mappers and some OO-RDBMS mappers
        (including Class::DBI, Alzabo, and DBIx::RecordSet in the former cate‐
        gory and Tangram and SPOPS in the latter) see the Perl Object-Oriented
        Persistence project pages at:
 
http://poop.sourceforge.net
 
        A similar page for Java toolkits can be found at:
 
http://c2.com/cgi-bin/wiki?ObjectRelationalToolComparison
 
        Mailing List
 
        The dbi-users mailing list is the primary means of communication among
        users of the DBI and its related modules. For details send email to:
 
         dbi-users-help@perl.org
 
        There are typically between 700 and 900 messages per month.  You have
        to subscribe in order to be able to post. However you can opt for a
        ’post-only’ subscription.
 
        Mailing list archives (of variable quality) are held at:
 
http://groups.google.com/groups?group=perl.dbi.users
http://www.xray.mpe.mpg.de/mailing-lists/dbi/
http://www.mail-archive.com/dbi-users%40perl.org/
 
        Assorted Related WWW Links
 
        The DBI "Home Page":
 
http://dbi.perl.org/
 
        Other DBI related links:
 
http://tegan.deltanet.com/~phlip/DBUIdoc.html
http://dc.pm.org/perl_db.html
http://wdvl.com/Authoring/DB/Intro/toc.html
http://www.hotwired.com/webmonkey/backend/tutorials/tutorial1.html
http://bumppo.net/lists/macperl/1999/06/msg00197.html
http://gmax.oltrelinux.com/dbirecipes.html
 
        Other database related links:
 
http://www.jcc.com/sql_stnd.html
http://cuiwww.unige.ch/OSG/info/FreeDB/FreeDB.home.html
http://www.connectionstrings.com/
 
        Security, especially the "SQL Injection" attack:
 
http://www.ngssoftware.com/research/papers.html
http://www.ngssoftware.com/papers/advanced_sql_injection.pdf
http://www.ngssoftware.com/papers/more_advanced_sql_injection.pdf
http://www.esecurityplanet.com/trends/article.php/2243461
http://www.spidynamics.com/papers/SQLInjectionWhitePaper.pdf
http://www.imperva.com/application_defense_center/white_papers/blind_sql_server_injection.html
http://online.securityfocus.com/infocus/1644
 
        Commercial and Data Warehouse Links
 
http://www.dwinfocenter.org
http://www.datawarehouse.com
http://www.datamining.org
http://www.olapcouncil.org
http://www.idwa.org
http://www.knowledgecenters.org/dwcenter.asp
 
        Recommended Perl Programming Links
 
http://language.perl.com/style/
 
        FAQ
 
        Please also read the DBI FAQ which is installed as a DBI::FAQ module.
        You can use perldoc to read it by executing the "perldoc DBI::FAQ" com‐
        mand.
 

AUTHORS

        DBI by Tim Bunce.  This pod text by Tim Bunce, J. Douglas Dunlop,
        Jonathan Leffler and others.  Perl by Larry Wall and the
        "perl5-porters".
 

COPYRIGHT

        The DBI module is Copyright (c) 1994-2004 Tim Bunce. Ireland.  All
        rights reserved.
 
        You may distribute under the terms of either the GNU General Public
        License or the Artistic License, as specified in the Perl README file.
        The DBI is free Open Source software. IT COMES WITHOUT WARRANTY OF ANY
        KIND.
 
        Support
 
        My consulting company, Data Plan Services, offers annual and multi-
        annual support contracts for the DBI. These provide sustained support
        for DBI development, and sustained value for you in return.  Contact me
        for details.
 
        Sponsor Enhancements
 
        The DBI Roadmap is available at
        <http://search.cpan.org/~timb/DBI/Roadmap.pod>
 
        If your company would benefit from a specific new DBI feature, please
        consider sponsoring its development.  Work is performed rapidly, and
        usually on a fixed-price payment-on-delivery basis.  Contact me for
        details.
 
        Using such targeted financing allows you to contribute to DBI develop‐
        ment, and rapidly get something specific and valuable in return.
 

ACKNOWLEDGEMENTS

        I would like to acknowledge the valuable contributions of the many peo‐
        ple I have worked with on the DBI project, especially in the early
        years (1992-1994). In no particular order: Kevin Stock, Buzz Moschetti,
        Kurt Andersen, Ted Lemon, William Hails, Garth Kennedy, Michael Pep‐
        pler, Neil S. Briscoe, Jeff Urlwin, David J. Hughes, Jeff Stander, For‐
        rest D Whitcher, Larry Wall, Jeff Fried, Roy Johnson, Paul Hudson,
        Georg Rehfeld, Steve Sizemore, Ron Pool, Jon Meek, Tom Christiansen,
        Steve Baumgarten, Randal Schwartz, and a whole lot more.
 
        Then, of course, there are the poor souls who have struggled through
        untold and undocumented obstacles to actually implement DBI drivers.
        Among their ranks are Jochen Wiedmann, Alligator Descartes, Jonathan
        Leffler, Jeff Urlwin, Michael Peppler, Henrik Tougaard, Edwin Pratomo,
        Davide Migliavacca, Jan Pazdziora, Peter Haworth, Edmund Mergl, Steve
        Williams, Thomas Lowery, and Phlip Plumlee. Without them, the DBI would
        not be the practical reality it is today.  I’m also especially grateful
        to Alligator Descartes for starting work on the first edition of the
        "Programming the Perl DBI" book and letting me jump on board.
 
        The DBI and DBD::Oracle were originally developed while I was Technical
        Director (CTO) of the Paul Ingram Group (www.ig.co.uk).  So I’d espe‐
        cially like to thank Paul for his generosity and vision in supporting
        this work for many years.
 

CONTRIBUTING

        As you can see above, many people have contributed to the DBI and
        drivers in many ways over many years.
 
        If you’d like to help then see <http://dbi.perl.org/contributing> and
        <http://search.cpan.org/~timb/DBI/Roadmap.pod>
 
        If you’d like the DBI to do something new or different then a good way
        to make that happen is to do it yourself and send me a patch to the
        source code that shows the changes. (But read "Speak before you patch"
        below.)
 
        Browsing the source code repository
 
http://svn.perl.org/modules/dbi/trunk (basic) or
http://svn.perl.org/viewcvs/modules/ (more useful)
 
        How to create a patch using Subversion
 
        The DBI source code is maintained using Subversion (a replacement for
        CVS, see <http://subversion.tigris.org/>). To access the source you’ll
        need to install a Subversion client. Then, to get the source code, do:
 
http://svn.perl.org/modules/dbi/trunk
 
        If it prompts for a username and password use your perl.org account if
        you have one, else just ’guest’ and ’guest’. The source code will be in
        a new subdirectory called "trunk".
 
        To keep informed about changes to the source you can send an empty
        email to svn-commit-modules-dbi-subscribe@perl.org after which you’ll
        get an email with the change log message and diff of each change
        checked-in to the source.
 
        After making your changes you can generate a patch file, but before you
        do, make sure your source is still upto date using:
 
          svn update
 
        If you get any conflicts reported you’ll need to fix them first.  Then
        generate the patch file from within the "trunk" directory using:
 
          svn diff > foo.patch
 
        Read the patch file, as a sanity check, and then email it to
        dbi-dev@perl.org.
 
        How to create a patch without Subversion
 
        Unpack a fresh copy of the distribution:
 
          tar xfz DBI-1.40.tar.gz
 
        Rename the newly created top level directory:
 
          mv DBI-1.40 DBI-1.40.your_foo
 
        Edit the contents of DBI-1.40.your_foo/* till it does what you want.
 
        Test your changes and then remove all temporary files:
 
          make test && make distclean
 
        Go back to the directory you originally unpacked the distribution:
 
          cd ..
 
        Unpack another copy of the original distribution you started with:
 
          tar xfz DBI-1.40.tar.gz
 
        Then create a patch file by performing a recursive "diff" on the two
        top level directories:
 
          diff -r -u DBI-1.40 DBI-1.40.your_foo > DBI-1.40.your_foo.patch
 
        Speak before you patch
 
        For anything non-trivial or possibly controversial it’s a good idea to
        discuss (on dbi-dev@perl.org) the changes you propose before actually
        spending time working on them. Otherwise you run the risk of them being
        rejected because they don’t fit into some larger plans you may not be
        aware of.
 

TRANSLATIONS

        A German translation of this manual (possibly slightly out of date) is
        available, thanks to O’Reilly, at:
 
http://www.oreilly.de/catalog/perldbiger/
 
        Some other translations:
 
http://cronopio.net/perl/                              - Spanish
http://member.nifty.ne.jp/hippo2000/dbimemo.htm        - Japanese
 

TRAINING

        References to DBI related training resources. No recommendation
        implied.
 
http://www.treepax.co.uk/
http://www.keller.com/dbweb/
 
        (If you offer professional DBI related training services, please send
        me your details so I can add them here.)
        See the DBI FAQ for a more comprehensive list of FAQs. Use the "perldoc
        DBI::FAQ" command to read it.
 
        Why doesn     t my CGI script work right?
 
        Read the information in the references below.  Please do not post CGI
        related questions to the dbi-users mailing list (or to me).
 
http://www.perl.com/cgi-bin/pace/pub/doc/FAQs/cgi/perl-cgi-faq.html
http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
http://www.boutell.com/faq/
http://www.perl.com/perl/faq/
 
        How can I maintain a WWW connection to a database?
 
        For information on the Apache httpd server and the "mod_perl" module
        see
 
http://perl.apache.org/
        Apache::DBI by E.Mergl@bawue.de
            To be used with the Apache daemon together with an embedded Perl
            interpreter like "mod_perl". Establishes a database connection
            which remains open for the lifetime of the HTTP daemon. This way
            the CGI connect and disconnect for every database access becomes
            superfluous.
 
        JDBC Server by Stuart ’Zen’ Bishop zen@bf.rmit.edu.au
            The server is written in Perl. The client classes that talk to it
            are of course in Java. Thus, a Java applet or application will be
            able to comunicate via the JDBC API with any database that has a
            DBI driver installed.  The URL used is in the form
            "jdbc:dbi://host.domain.etc:999/Driver/DBName".  It seems to be
            very similar to some commercial products, such as jdbcKona.
 
        Remote Proxy DBD support
            As of DBI 1.02, a complete implementation of a DBD::Proxy driver
            and the DBI::ProxyServer are part of the DBI distribution.
 
        SQL Parser
            See also the SQL::Statement module, SQL parser and engine.
 

Sections

What does Ubuntu mean?
Ubuntu is an African word meaning 'Humanity to others', or 'I am what I am because of who we all are'. The Ubuntu distribution brings the spirit of Ubuntu to the software world.