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DBI(3)         User Contributed Perl Documentation         DBI(3)

NAME
       DBI - Database independent interface for Perl

SYNOPSIS
         use DBI;

         @driver_names = DBI->available_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);

         $ary_ref  = $dbh->selectrow_arrayref($statement);
         @row_ary  = $dbh->selectrow_array($statement);
         $hash_ref = $dbh->selectrow_hashref($statement);

         $sth = $dbh->prepare($statement);
         $sth = $dbh->prepare_cached($statement);

         $rv = $sth->bind_param($p_num, $bind_value);
         $rv = $sth->bind_param($p_num, $bind_value, $bind_type);
         $rv = $sth->bind_param($p_num, $bind_value, \%attr);

         $rv = $sth->execute;
         $rv = $sth->execute(@bind_values);

         $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( { ... } );
         $ary_ref  = $sth->fetchall_arrayref( [ ... ] );

         $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;

       This synopsis above only lists the major methods.

       GETTING HELP

       If you have questions about DBI, you can get help from the
        mailing list.  You can subscribe to the
       list by emailing:

         

       Also worth a visit is the DBI home page at:

         http://dbi.perl.org/

       Before asking any questions, reread this document, consult
       the archives and read the DBI FAQ. The archives are listed
       at the end of this document and on the DBI home page.  The
       FAQ is installed as a DBI::FAQ module so you can read it
       by executing "perldoc DBI::FAQ".

       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 personally. The dbi-
       users mailing list has lots of experienced people who
       should be able to help you if you need it.

       NOTE

       This is the DBI specification that corresponds to the DBI
       version 1.21 ("$Date: 2002/02/07 03:00:53 $").

       The DBI specification is evolving at a steady pace, so
       it's important to check that you have the latest copy.

       The significant user-visible changes in each release are
       documented in the DBI::FAQ module so you can read them by
       executing "perldoc DBI::Changes".

       Note also that whenever the DBI changes, the drivers take
       some time to catch up. Recent versions of the DBI have
       added new features (generally marked NEW in the text) that
       may not yet be supported by the drivers you use. Talk to
       the authors of those drivers if you need the new features.

       Extensions to the DBI use the "DBIx::*" namespace. See
       "Naming Conventions and Name Space" and:

         http://search.cpan.org/search?mode=module&query=DBIx%3A%3A

DESCRIPTION
       The DBI is a database access module for the Perl program-
       ming language.  It defines a set of methods, variables,
       and conventions that provide a consistent database inter-
       face, independent of the actual database being used.

       It is important to remember that the DBI is just an inter-
       face.  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 oper-
       ate within.

       Architecture of a DBI Application

                    ||
                         .-.   .--------------.   .-------------.
         .-------.       | |---| 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 interface 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 implementations for methods,
       and many other non-database specific duties.

       Each driver contains implementations of the DBI methods
       using the private interface functions of the corresponding
       database engine.  Only authors of sophisti-
       cated/multi-database applications or generic library func-
       tions 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 recom-
       mended.)

       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 con-
       nect at the start of your program and disconnect at the
       end.

       Explicitly defining the required "AutoCommit" behavior is
       strongly recommended and may become mandatory in a later
       version.  This determines whether changes are automati-
       cally committed to the database when executed, or need to
       be explicitly committed later.

       The DBI allows an application to "prepare" statements for
       later execution.  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" state-
       ment is:

         prepare,
           execute,
           execute,
           execute.

       for example:

         $sth = $dbh->prepare("INSERT INTO table(foo,bar,baz) VALUES (?,?,?)");

         while() {
           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 accu-
       racy.  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, pre-
       sumably based on the locale. If a driver needs to set a
       flag to get that behavior, 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 handle ($sth), although some databases and
       drivers do support this (notably Sybase and SQL Server).

       Non-sequential record reads are not supported in this ver-
       sion 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 functions 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" parameters 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 mod-
       ules use the "DBIx::" namespace (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 sig-
       nify 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 lowercase 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).

       Driver Specific Prefix Registry:

         ad_      DBD::AnyData
         ado_     DBD::ADO
         best_    DBD::BestWins
         csv_     DBD::CSV
         db2_     DBD::DB2
         f_       DBD::File
         file_    DBD::TextFile
         ib_      DBD::InterBase
         ing_     DBD::Ingres
         ix_      DBD::Informix
         msql_    DBD::mSQL
         mysql_   DBD::mysql
         odbc_    DBD::ODBC
         ora_     DBD::Oracle
         pg_      DBD::Pg
         proxy_   DBD::Proxy
         rdb_     DBD::RDB
         sapdb_   DBD::SAP_DB
         solid_   DBD::Solid
         syb_     DBD::Sybase
         tdat_    DBD::Teradata
         tuber_   DBD::Tuber
         uni_     DBD::Unify
         xbase_   DBD::XBase

       SQL - A Query Language

       Most DBI drivers require applications to use a dialect of
       SQL (Structured Query Language) to interact with the
       database engine.  The following links provide useful
       information and further links about SQL:

         http://www.altavista.com/query?q=sql+tutorial
         http://www.jcc.com/sql_stnd.html
         http://www.contrib.andrew.cmu.edu/~shadow/sql.html

       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 "And the rest" and "Intergalactic dataspeak"
       links for the SQL history.

       Placeholders and Bind Values

       Some drivers support placeholders and bind values.  Place-
       holders, also called parameter markers, are used to indi-
       cate 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.

       When using placeholders with the SQL "LIKE" qualifier, you
       must remember 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", can be used to indicate null
       values.  However, care must be taken in the particular
       case of trying to use null values to qualify a "SELECT"
       statement. Consider:

         SELECT description FROM products WHERE product_code = ?

       Binding an "undef" (NULL) to the placeholder will not
       select rows which have a NULL "product_code"! 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 product_code IS NULL"" and to make that
       general you have to say:

         ... WHERE (product_code = ? OR (? IS NULL AND product_code IS NULL))

       and bind the same value to both placeholders.

       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 typically 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 state-
       ment. 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_column" method, which is used to asso-
       ciate Perl variables with the output columns of a "SELECT"
       statement.

THE DBI PACKAGE AND CLASS
       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 produced 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 possible uses.

       Note that just because the DBI defines a named constant
       for a given data type doesn't mean that drivers will sup-
       port that data type.

       DBI Class Methods

       The following methods are provided by the DBI class:

       "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-">"dis-
           connect" to terminate the connection.

           If the connect fails (see below), it returns "undef"
           and sets both $DBI::err and $DBI::errstr. (It does not
           set $!, etc.) 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 should begin with
           ""dbi:"driver_name":"". The driver_name specifies the
           driver that will be used to make the connection. (Let-
           ter case is significant.)

           As a convenience, if the $data_source parameter is
           undefined or empty, the DBI will substitute the value
           of the environment variable "DBI_DSN".  If just the
           driver_name part is empty (i.e., the $data_source pre-
           fix 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:[email protected]: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 requirement 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.
           (Where a driver author needs to define a syntax for
           the $data_source, it is recommended that they follow
           the ODBC style, shown in the last example above.)

           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:

             dbi:Proxy:$ENV{DBI_AUTOPROXY};dsn=$data_source

           and passed to the DBD::Proxy module. "DBI_AUTOPROXY"
           is typically set as ""hostname=...;port=..."". 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 vari-
           ables, respectively.  The DBI will warn if the envi-
           ronment variables are not defined.  However, the
           everyday use of these environment variables is not
           recommended for security reasons. The mechanism is
           primarily intended to simplify testing.

           "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.

           The $data_source argument (with the ""dbi:...:"" pre-
           fix 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 information.)  However, it is
           strongly recommended that you explicitly define "Auto-
           Commit" rather than rely on the default. Future ver-
           sions of the DBI may issue a warning if "AutoCommit"
           is not explicitly defined.

           The "\%attr" parameter can be used to alter the
           default settings of "PrintError", "RaiseError", "Auto-
           Commit", and other attributes. For example:

             $dbh = DBI->connect($data_source, $user, $pass, {
                   PrintError => 0,
                   AutoCommit => 0
             });

           You can also define connection attribute values within
           the $data_source parameter. For example:

             dbi:DriverName(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 estab-
           lish the connection. The only useful values are 'con-
           nect', 'connect_cached', or some specialized case like
           'Apache::DBI::connect' (which is automatically the
           default when running within Apache).

           Where possible, each session ($dbh) is independent
           from the transactions in other sessions. This is use-
           ful when you need to hold cursors open across transac-
           tions--for example, if you use one session 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 argu-
           ment 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 be with-
           drawn in a future version of DBI.

       "connect_cached" NEW
             $dbh = DBI->connect_cached($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 parameters. 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.

           Note that the behavior of this method differs in sev-
           eral respects from the behavior of presistent connec-
           tions implemented by Apache::DBI.

           Caching can be useful in some applications, but it can
           also cause problems and should be used with care. The
           exact behavior of this method is liable to change, so
           if you intend to use it in any production applications
           you should discuss your needs on the dbi-users mailing
           list.

           The cache can be accessed (and cleared) via the
           "CachedKids" attribute.

       "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 earlier directo-
           ries. Passing a true value for $quiet will inhibit the
           warning.

       "data_sources"
             @ary = DBI->data_sources($driver);
             @ary = DBI->data_sources($driver, \%attr);

           Returns a list of all data sources (databases) avail-
           able via the named driver.  If $driver is empty or
           "undef", then the value of the "DBI_DRIVER" environ-
           ment variable is used.

           The driver will be loaded if it hasn't been already.
           Note that if the driver loading fails then it dies
           with an error message that includes the string
           ""install_driver"" and the underlying problem.

           Data sources are returned in a form suitable for pass-
           ing 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 incomplete list or may require
           driver-specific attributes, such as a connected
           database handle, to be supplied.

       "trace"
             DBI->trace($trace_level)
             DBI->trace($trace_level, $trace_filename)

           DBI trace information can be enabled for all handles
           using the "trace" DBI class method. To enable trace
           information for a specific handle, use the similar
           "$h-">"trace" method described elsewhere.

           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.
                 Also includes DBI mutex information when using threaded Perl.
             5 and above - 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 (up to 9) 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 use-
           ful. Much of the trace output is formatted using the
           "neat" function, so strings in the trace output may be
           edited and truncated.

           Initially trace output is written to "STDERR".  If
           $trace_filename is specified and can be opened in
           append mode then all trace output (including that from
           other handles) is redirected to that file.  A warning
           is generated is 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_file-
           name is undefined, then trace output is sent to
           "STDERR" and the previous trace file is closed.  The
           "trace" method returns the previous tracelevel.

           See also the "$h-">"trace" and "$h-">"trace_msg" meth-
           ods and the "DEBUGGING" section for information about
           the "DBI_TRACE" environment variable.

       DBI Utility Functions

       In addition to the methods listed in the previous section,
       the DBI package also provides these utility functions:

       "neat"
             $str = DBI::neat($value, $maxlen);

           Return a string containing a neat (and tidy) represen-
           tation 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). Unprintable characters 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 typically not be used for
           formatting values for database use.  (See also
           "quote".)

       "neat_list"
             $str = DBI::neat_list(\@listref, $maxlen, $field_sep);

           Calls "DBI::neat" on each element of the list and
           returns a string containing the results joined with
           $field_sep. $field_sep defaults to ", ".

       "looks_like_number"
             @bool = DBI::looks_like_number(@array);

           Returns true for each element that looks like a num-
           ber.  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 algorithm 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 nega-
           tive (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 docu-
           mentation 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.

METHODS COMMON TO ALL HANDLES
       The following methods can be used by all types of DBI han-
       dles.

       "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 most DBI method
           calls, so the value only has a short lifespan. Also,
           most drivers share the same error variables across all
           their handles, so calling a method on one handle will
           typically reset the error on all the other handles
           that are children of that driver.

           If you need to test for individual errors and have
           your program be portable to different database
           engines, then you'll need to determine what the corre-
           sponding error codes are for all those engines and
           test for all of them.

       "errstr"
             $str = $h->errstr;

           Returns the native database engine error message from
           the last driver method called. This has the same
           lifespan issues as the "err" method described above.

       "state"
             $str = $h->state;

           Returns an error code in the standard SQLSTATE five
           character format.  Note that the specific success code
           00000 is translated to '' (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.

       "set_err" NEW

             $rv = $h->set_err($err, $errstr);
             $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 will trigger the normal DBI error han-
           dling mechanisms, such as "RaiseError" and "HandleEr-
           ror", if they are enabled.  This method is typically
           only used by DBI drivers and DBI subclasses.

           The $method parameter provides an alternate method
           name, instead of the fairly unhelpful '"set_err"', for
           the "RaiseError"/"PrintError" error string.

           The "set_err" method normally returns undef.  The $rv
           parameter provides an alternate return value. The
           "HandleError" subroutine can access and alter this
           value.

       "trace"
             $h->trace($trace_level);
             $h->trace($trace_level, $trace_filename);

           DBI trace information can be enabled for a specific
           handle (and any future children of that handle) by
           setting the trace level using the "trace" method.

           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 (up to 9) are
           best reserved for investigating a specific problem,
           when you need to see "inside" the driver and DBI.  Set
           $trace_level to 0 to disable the trace.

           The trace output is detailed and typically very use-
           ful. Much of the trace output is formatted using the
           "neat" function, so strings in the trace output may be
           edited and truncated.

           Initially, trace output is written to "STDERR".  If
           $trace_filename is specified, then the file is opened
           in append mode and all trace output (including that
           from other handles) is redirected to that file.  Fur-
           ther calls to trace without a $trace_filename do not
           alter where the trace output is sent. If $trace_file-
           name is undefined, then trace output is sent to
           "STDERR" and the previous trace file is closed.

           See also the "DBI-">"trace" method, the
           "$h-">"{TraceLevel}" attribute, and "DEBUGGING" for
           information about the "DBI_TRACE" environment vari-
           able.

       "trace_msg"
             $h->trace_msg($message_text);
             $h->trace_msg($message_text, $min_level);

           Writes $message_text to the trace file if trace is
           enabled for $h or for the DBI as a whole. Can also be
           called as "DBI-">"trace_msg($msg)".  See "trace".

           If $min_level is defined, then the message is output
           only if the trace level is equal to or greater than
           that level. $min_level defaults to 1.

       "func"
             $h->func(@func_arguments, $func_name);

           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.

           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.

ATTRIBUTES COMMON TO ALL HANDLES
       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 state-
       ment handle do not affect the parent database handle and
       changes to the database handle do not affect existing
       statement handles, only future ones.

       Attempting to set or get the value of an unknown attribute
       is fatal, 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)
           Enables useful warnings for certain bad practices.
           Enabled by default. Some emulation layers, especially
           those for Perl 4 interfaces, disable warnings.  Since
           warnings are generated using the Perl "warn" function,
           they can be intercepted using the Perl $SIG{__WARN__}
           hook.

       "Active" (boolean, read-only)
           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 ("$dbh-">"disconnect" sets "Active" off).
           For a statement handle it typically means that the
           handle is a "SELECT" that may have more data to fetch.
           (Fetching all the data or calling "$sth-">"finish"
           sets "Active" off.)

       "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 statement handles that
           were created from that database handle.

       "ActiveKids" (integer, read-only)
           Like "Kids", but only counting those that are "Active"
           (as above).

       "CachedKids" (hash ref)
           For a database handle, returns a reference to the
           cache (hash) of statement handles created by the "pre-
           pare_cached" method.  For a driver handle, returns a
           reference to the cache (hash) of database handles cre-
           ated by the "connect_cached" method.

       "CompatMode" (boolean, inherited)
           Used by emulation layers (such as Oraperl) to enable
           compatible behavior in the underlying driver (e.g.,
           DBD::Oracle) for this handle. Not normally set by
           application code.

       "InactiveDestroy" (boolean)
           This attribute can be used to disable the database
           engine related effect of DESTROYing a handle (which
           would normally close a prepared statement or discon-
           nect from the database etc).

           For a database handle, this attribute does not disable
           an explicit call to the disconnect method, only the
           implicit call from DESTROY.

           The default value, false, means that a handle will be
           automatically destroyed when it passes out of scope.
           A true value disables automatic destruction. (Think of
           the name as meaning 'inactive the DESTROY method'.)

           This attribute is specifically designed for use in
           Unix applications that "fork" child processes. Either
           the parent or the child process, but not both, should
           set "InactiveDestroy" on all their shared handles.
           Note that some databases, including Oracle, don't sup-
           port passing a database connection across a fork.

       "PrintError" (boolean, inherited)
           This 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::ErrorWrap.

       "RaiseError" (boolean, inherited)
           This 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 ([email protected]) { ... }" block to
           handle the caught exception. In that eval block the
           $DBI::lasth variable can be useful for diagnosis and
           reporting.  For example, $DBI::lasth->{Type} and
           $DBI::lasth->{Statement}.

           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".

           Sadly, this doesn't work for Perl versions up to and
           including 5.004_04.  Even more sadly, for Perl 5.5 and
           5.6.0 it does work but leaks memory!  For backwards
           compatibility, you could just use "eval { ... }"
           instead.

       "HandleError" (code ref, inherited) NEW
           This attribute can be used to provide your own alter-
           native behaviour in case of errors. If set to a refer-
           ence to a subroutine 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 "PrintEr-
           ror" 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 normal.

           For example, to get 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 han-
           dlers 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 hide an error, to
           a limited 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(0,"");  # 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 gen-
           eral use!  If you find a good use for it then please
           let me know.

       "ShowErrorStatement" (boolean, inherited) NEW
           This attribute can be used to cause the relevant
           Statement text to be appended to the error messages
           generated by the "RaiseError" and "PrintError"
           attributes. Only applies to errors on statement han-
           dles plus the prepare() and do() database handle meth-
           ods.  (The exact format of the appended text is sub-
           ject to change.)

       "TraceLevel" (integer, inherited) NEW
           This attribute can be used as an alternative to the
           "trace" method to set the DBI trace level for a spe-
           cific handle.

       "FetchHashKeyName" (string, inherited)
           This attribute is used to specify which attribute name
           the fetchrow_hashref() method should use to get the
           field names for the hash keys. For historical reasons
           it defaults to '"NAME"' but it is recommended to set
           it to '"NAME_lc"' or '"NAME_uc"' according to your
           preference. It can only be set for driver and database
           tables.  For statement handles the value is frozen
           when prepare() is called.

       "ChopBlanks" (boolean, inherited)
           This 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
           behavior should set the attribute as needed. Emulation
           interfaces should set the attribute to match the
           behavior of the interface they are emulating.

           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)
           This attribute may be used to control the maximum
           length of long fields ("blob", "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. ("fetch" should return "undef" 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 digits.  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".

           Note that the value used here has a direct effect on
           the memory used by the application, so don't be too
           generous.

           See "LongTruncOk" for more information on truncation
           behavior.

       "LongTruncOk" (boolean, inherited)
           This 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.  (Applications 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 truncation,
           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".

       "Taint" (boolean, inherited)
           If this attribute is set to a true value and Perl is
           running in taint mode (e.g., started with the "-T"
           option), then all data fetched from the database is
           tainted, and 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
           Taint 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 suggestions for changes.

       "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 retreive any attribute which has a
           name starting with ""private_"".

           It is strongly recommended that you use just one pri-
           vate 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} = { ... };

DBI DATABASE HANDLE OBJECTS
       This section covers the methods and attributes associated
       with database handles.

       Database Handle Methods

       The following methods are specified for DBI database han-
       dles:

       "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 number 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
           statement 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
           "execute" 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{...}" opera-
           tor if you want to interpolate variables into the
           string.  See "Quote and Quote-like Operators" in per-
           lop for more details.

       "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. If called in a scalar context, it
           returns the first field of the first row. 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.

           In a scalar context, "selectrow_array" returns the
           value of the first field. An "undef" is returned if
           there are no matching rows or an error occurred. Since
           that "undef" can't be distinguished from an "undef"
           returned because the first field value was NULL, call-
           ing "selectrow_array" in a scalar context should be
           used with caution.

       "selectrow_arrayref"
             $ary_ref = $dbh->selectrow_array($statement);
             $ary_ref = $dbh->selectrow_array($statement, \%attr);
             $ary_ref = $dbh->selectrow_array($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 previously prepared statement han-
           dle, 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 previously prepared statement han-
           dle, in which case the "prepare" is skipped.

           If any method fails, and "RaiseError" is not set,
           "selectrow_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 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 discover if the
           data is complete or was truncated due to an error.

           The "fetchall_arrayref" method called by "selec-
           tall_arrayref" 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".

       "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 for each row.
           The key for each row entry is specified by $key_field.
           The value is a reference to a hash returned by
           "fetchrow_hashref".

           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 "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.

       "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 reference 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 col-
           umn, 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

       "prepare"
             $sth = $dbh->prepare($statement)          or die $dbh->errstr;
             $sth = $dbh->prepare($statement, \%attr)  or die $dbh->errstr;

           Prepares a single 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 "$sth-">"exe-
           cute" is called. Such drivers are unlikely to give
           much useful information about the statement, such as
           "$sth-">"{NUM_OF_FIELDS}", until after "$sth-">"exe-
           cute" 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 "Place-
           holders"). 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 previous statement.

           Some command-line SQL tools use statement terminators,
           like a semicolon, 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, $allow_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 values, then the corre-
           sponding cached $sth will be returned without contact-
           ing the database server.

           This caching can be useful in some applications, but
           it can also cause problems and should be used with
           care. If the cached $sth being returned is active
           (i.e., is a "SELECT" that may still have data to be
           fetched) then a warning will be generated and "finish"
           will be called for you.  The warning can be suppressed
           by setting $allow_active to true.  The cache can be
           accessed (and cleared) via the "CachedKids" attribute.

           Here are some examples of "prepare_cached":

             sub insert_hash {
               my ($table, $field_values) = @_;
               my @fields = sort keys %$field_values; # sort required
               my @values = @{$field_values}{@fields};
               my $sql = sprintf "insert into %s (%s) values (%s)",
                   $table, join(",", @fields), join(",", ("?")[email protected]);
               my $sth = $dbh->prepare_cached($sql);
               return $sth->execute(@values);
             }

             sub search_hash {
               my ($table, $field_values) = @_;
               my @fields = sort keys %$field_values; # sort required
               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);
             }

       "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 "rollback ineffective with AutoCommit" warn-
           ing.

           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 "rollback", "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 disconnect-
           ing.

           The transaction behavior of the "disconnect" method
           is, sadly, undefined.  Some database systems (such as
           Oracle and Ingres) will automatically commit any out-
           standing 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 "roll-
           back" to undo any uncommitted changes. This is vital
           behavior to ensure that incomplete transactions don't
           get committed simply because Perl calls "DESTROY" on
           every object before exiting. Also, do not rely on the
           order of object destruction during "global destruc-
           tion", 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 discon-
           necting.

           If you disconnect from a database while you still have
           active statement handles, you will get a warning. The
           statement handles should either be cleared (destroyed)
           before disconnecting, or the "finish" method should be
           called on each one.

       "ping"
             $rc = $dbh->ping;

           Attempts to determine, in a reasonably efficient way,
           if the database server is still running and the con-
           nection 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 genuine 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" NEW
           Warning: This method is experimental and may change.

             $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 infor-
           mation 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 curently doesn't provide a name to number map-
           ping for the information type codes or the results.
           Applications are expected to use the integer values
           directly, with the name in a comment, or define their
           own named values using something like the constant
           pragma.

           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" NEW
           Warning: This method is experimental and may change.

             $sth = $dbh->table_info( $catalog, $schema, $table, $type );
             $sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
             $sth = $dbh->table_info( \%attr ); # old style

           Returns an active statement handle that can be used to
           fetch information about tables and views that exist in
           the database.

           The old style interface passes all the parameters as a
           reference to an attribute hash with some or all of the
           following attributes:

             %attr = (
                  TABLE_CAT   => $catalog  # String value of the catalog name
                , TABLE_SCHEM => $schema   # String value of the schema name
                , TABLE_NAME  => $table    # String value of the table name
                , TABLE_TYPE  => $type     # String value of the table type(s)
             );

           The old style interface is deprecated and will be
           removed in a future version.

           The support for the selection criteria is driver spe-
           cific. 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 arguments $catalog, $schema and $table may accept
           search patterns according to the database/driver, for
           example: $table = '%FOO%'; Remember that the under-
           score 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 optionally 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 con-
           tains a list of table types.

           The statement handle returned has at least the follow-
           ing 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 spe-
           cific 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" and "Standards Reference Informa-
           tion".

       "column_info" NEW
           Warning: This method is experimental and may change.

             $sth = $dbh->column_info( $catalog, $schema, $table, $column );

           Returns an active statement handle that can be used to
           fetch information about columns in specified tables.

           The arguments $schema, $table and $column may accept
           search patterns 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 follow-
           ing 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 appli-
           cable 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 column 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 characters 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 spe-
           cific information 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, SQL-
           Columns provides more metadata.

           See also "Standards Reference Information".

       "primary_key_info" NEW
           Warning: This method is experimental and may change.

             $sth = $dbh->primary_key_info( $catalog, $schema, $table );

           Returns an active statement handle that can be used to
           fetch information about columns that make up the pri-
           mary 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;

           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 follow-
           ing 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 "Standards Reference Information".

       "primary_key" NEW
           Warning: This method is experimental and may change.

             @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.

       "foreign_key_info" NEW
           Warning: This method is experimental and may change.

             $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
                                          , $fk_catalog, $fk_schema, $fk_table );

           Returns an active statement handle that can be used to
           fetch information about foreign keys in and/or refer-
           encing the specified table(s).  The arguments don't
           accept search patterns (unlike table_info()).

           $pk_catalog, $pk_schema, $pk_table identify the pri-
           mary (unique) key table (PKT).

           $fk_catalog, $fk_schema, $fk_table identify the for-
           eign 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 implementation-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 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.

           PKTABLE_SCHEM  ( UK_TABLE_SCHEM    ): The primary
           (unique) key table schema identifier.  This field is
           NULL ("undef") if not applicable to the data source,
           and empty if not applicable to the table.

           PKTABLE_NAME   ( UK_TABLE_NAME     ): The primary
           (unique) key table identifier.

           PKCOLUMN_NAME  (UK_COLUMN_NAME    ): The primary
           (unique) key column 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 appli-
           cable 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 identifier.

           FKCOLUMN_NAME  ( FK_COLUMN_NAME    ): The foreign key
           column identifier.

           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 deferrabil-
           ity of the foreign 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 PRIMARY 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 "Standards Reference Information".

       "tables" NEW
           Warning: This method is experimental and may change.

             @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 cata-
           log/schema prefix.

           See "table_info" for a description of the parameters.

           If "$dbh-">"get_info(29)" returns true (29 is
           SQL_IDENTIFIER_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.

       "type_info_all"
           Warning: This method is experimental and may change.

             $type_info_all = $dbh->type_info_all;

           Returns a reference to an array which holds informa-
           tion 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,
                   NUM_PREC_RADIX    => 15,
               },
               [ '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
               ],
             ];

           Note that 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 documen-
           tation for the "type_info" method. The index values
           shown above (e.g., "NULLABLE ="> 6) are for illustra-
           tion only. Drivers may define the fields with a dif-
           ferent order.

           This method is not normally used directly. The
           "type_info" method provides a more useful interface to
           the data.

           Even though an 'index' hash is provided, all the field
           names in the index hash defined above will always have
           the index values defined above.  This is defined
           behaviour so that you don't need to rely on the index
           hash, which is handy because the lettercase of the
           keys is not defined. It is usually uppercase, as show
           here, but drivers are free to 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 specifica-
           tion.

       "type_info"
           Warning: This method is experimental and may change.

             @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 vari-
           ants 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 con-
           ventions as the rest of the DBI (see "Naming Conven-
           tions and Name Space"). The following items should
           exist:

           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 bytes.

               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 characters.  NULL ("undef") is returned
               for data types where this is not applicable.

           CREATE_PARAMS (string)
               Parameter names for data type definition. For
               example, "CREATE_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_INTERVAL"
               or "SQL_DATETIME", and the "SQL_DATETIME_SUB"
               field below will return the subcode for the spe-
               cific interval or datetime data type. If this
               field is NULL, then the driver does not support or
               report on interval or date 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").

           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 statement, 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 deter-
           mine the required quoting behavior by using the infor-
           mation 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 pos-
           sible input (such as binary data or data containing
           newlines), and is not related in any way with escaping
           or quoting shell meta-characters. There is no need to
           quote values being used with "Placeholders and Bind
           Values".

       "quote_identifier"
             $sql = $dbh->quote_identifier( $name );
             $sql = $dbh->quote_identifier( $name1, $name2, $name3, \%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 catalog name and special rules may be applied
           based on what "get_info" returns for SQL_CATA-
           LOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCATION
           (114).  For example, for Oracle:

             $id = $dbh->quote_identifier( 'link', 'schema', 'table' );

           would return "schema"."table"@"link".

       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
       is fatal, 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 automati-
           cally occur within a "transaction", 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 behavior
           can set "$dbh-">"{AutoCommit} = 0" (or set "AutoCom-
           mit" 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).

           * 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 "AutoCom-
           mit" is in effect.

           * Databases in which a transaction is always active

           These are typically mainstream commercial relational
           databases with "ANSI standard" transaction behavior.
           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 operation. In other words, calling
           "commit" or "rollback" explicitly while "AutoCommit"
           is on would be ineffective because the changes would
           have already been commited.

           Changing "AutoCommit" from off to on should issue a
           "commit" in most drivers.

           Changing "AutoCommit" from on to off should have no
           immediate effect.

           For databases which don't support a specific auto-com-
           mit mode, the driver has to commit each statement
           automatically using an explicit "COMMIT" after it com-
           pletes successfully (and roll it back using an
           explicit "ROLLBACK" if it fails).  The error informa-
           tion reported to the application will correspond to
           the statement which was executed, 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 DBI driver will automatically begin a
           transaction when "AutoCommit" is turned off (from the
           default "on" state) and will automatically begin
           another transaction after a "commit" or "rollback".
           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 recom-
           mended 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 recom-
           mended 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 [email protected] 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 setting "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

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