DBI (manpage)

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Manpage

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);
        @row_ary  = $dbh->selectrow_array($statement);
        $ary_ref  = $dbh->selectrow_arrayref($statement);
        $hash_ref = $dbh->selectrow_hashref($statement);
        $sth = $dbh->prepare($statement);
        $sth = $dbh->prepare_cached($statement);
        $rc = $sth->bind_param($p_num, $bind_value);
        $rc = $sth->bind_param($p_num, $bind_value, $bind_type);
        $rc = $sth->bind_param($p_num, $bind_value, \%attr);
        $rv = $sth->execute;
        $rv = $sth->execute(@bind_values);
        $rv = $sth->execute_array(\%attr, ...);
        $rc = $sth->bind_col($col_num, \$col_variable);
        $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
        @row_ary  = $sth->fetchrow_array;
        $ary_ref  = $sth->fetchrow_arrayref;
        $hash_ref = $sth->fetchrow_hashref;
        $ary_ref  = $sth->fetchall_arrayref;
        $ary_ref  = $sth->fetchall_arrayref( $slice, $max_rows );
        $hash_ref = $sth->fetchall_hashref( $key_field );
        $rv  = $sth->rows;
        $rc  = $dbh->begin_work;
        $rc  = $dbh->commit;
        $rc  = $dbh->rollback;
        $quoted_string = $dbh->quote($string);
        $rc  = $h->err;
        $str = $h->errstr;
        $rv  = $h->state;
        $rc  = $dbh->disconnect;

The synopsis above only lists the major methods and parameters.

GETTING HELP

If you have questions about DBI, or DBD driver modules, you can get help from the dbi-usersspam@spamperlspam.spamorg mailing list. You can get help on subscribing and using the list by emailing dbi-users-helpspam@spamperlspam.spamorg.

(To help you make the best use of the dbi-users mailing list, and any other lists or forums you may use, I strongly recommend that you read "How To Ask Questions The Smart Way" by Eric Raymond: <http://www.catb.org/~esr/faqs/smart-questions.html>)

The DBI home page at <http://dbi.perl.org/> is always worth a visit and includes an FAQ and links to other resources.

Before asking any questions, reread this document, consult the archives and read the DBI FAQ. The archives are listed at the end of this document and on the DBI home page. An FAQ is installed as a DBI::FAQ module so you can read it by executing "perldoc DBI::FAQ". However the DBI::FAQ module is currently (2004) outdated relative to the online FAQ on the DBI home page.

This document often uses terms like references, objects, methods. If you're not familar with those terms then it would be a good idea to read at least the following perl manuals first: perlreftut, perldsc, perllol, and perlboot.

Please note that Tim Bunce does not maintain the mailing lists or the web page (generous volunteers do that). So please don't send mail directly to him; he just doesn't have the time to answer questions personally. The dbi-users mailing list has lots of experienced people who should be able to help you if you need it. If you do email Tim he's very likely to just forward it to the mailing list.

NOTES

This is the DBI specification that corresponds to the DBI version 1.46.

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

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

Some DBI changes require changes in the drivers, but the drivers can take some time to catch up. Newer versions of the DBI have added features that may not yet be supported by the drivers you use. Talk to the authors of your drivers if you need a new feature that's not yet supported.

Features added after DBI 1.21 (February 2002) are marked in the text with the version number of the DBI release they first appeared in.

Extensions to the DBI API often use the "DBIx::*" namespace. See "Naming Conventions and Name Space". DBI extension modules can be found at <http://search.cpan.org/search?mode=module&query=DBIx>. And all modules related to the DBI can be found at <http://search.cpan.org/search?query=DBI&mode=all>.

DESCRIPTION

The DBI is a database access module for the Perl programming language. It defines a set of methods, variables, and conventions that provide a consistent database interface, independent of the actual database being used.

It is important to remember that the DBI is just an interface. The DBI is a layer of "glue" between an application and one or more database driver modules. It is the driver modules which do most of the real work. The DBI provides a standard interface and framework for the drivers to operate within.

Architecture of a DBI Application

                   |<- Scope of DBI ->|
                        .-.   .--------------.   .-------------.
        .-------.       | |---| XYZ Driver   |---| XYZ Engine  |
        | Perl  |       | |   `--------------'   `-------------'
        | script|  |A|  |D|   .--------------.   .-------------.
        | using |--|P|--|B|---|Oracle Driver |---|Oracle Engine|
        | DBI   |  |I|  |I|   `--------------'   `-------------'
        | API   |       | |...
        |methods|       | |... Other drivers
        `-------'       | |...
                        `-'

The API, or Application Programming Interface, defines the call 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 sophisticated/multi-database applications or generic library functions need be concerned with drivers.

Notation and Conventions

The following conventions are used in this document:

        $dbh    Database handle object
        $sth    Statement handle object
        $drh    Driver handle object (rarely seen or used in applications)
        $h      Any of the handle types above ($dbh, $sth, or $drh)
        $rc     General Return Code  (boolean: true=ok, false=error)
        $rv     General Return Value (typically an integer)
        @ary    List of values returned from the database, typically a row of data
        $rows   Number of rows processed (if available, else -1)
        $fh     A filehandle
        undef   NULL values are represented by undefined values in Perl
        \%attr  Reference to a hash of attribute values passed to methods

Note that Perl will automatically destroy database and statement handle objects if all references to them are deleted.

Outline Usage

To use DBI, first you need to load the DBI module:

        use DBI;
        use strict;

(The "use strict;" isn't required but is strongly recommended.)

Then you need to "connect" to your data source and get a handle for that connection:

        $dbh = DBI->connect($dsn, $user, $password,
                            { RaiseError => 1, AutoCommit => 0 });

Since connecting can be expensive, you generally just connect at the start of your program and disconnect at the end.

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

The DBI allows an application to "prepare" statements for later execu tion. A prepared statement is identified by a statement handle held in a Perl variable. We'll call the Perl variable $sth in our examples.

The typical method call sequence for a "SELECT" statement is:

        prepare,
          execute, fetch, fetch, ...
          execute, fetch, fetch, ...
          execute, fetch, fetch, ...

for example:

        $sth = $dbh->prepare("SELECT foo, bar FROM table WHERE baz=?");
        $sth->execute( $baz );
        while ( @row = $sth->fetchrow_array ) {
          print "@row\n";
        }

The typical method call sequence for a non-"SELECT" statement is:

        prepare,
          execute,
          execute,
          execute.

for example:

        $sth = $dbh->prepare("INSERT INTO table(foo,bar,baz) VALUES (?,?,?)");
        while(<CSV>) {
          chomp;
          my ($foo,$bar,$baz) = split /,/;
              $sth->execute( $foo, $bar, $baz );
        }

The "do()" method can be used for non repeated non-"SELECT" statement (or with drivers that don't support placeholders):

        $rows_affected = $dbh->do("UPDATE your_table SET foo = foo + 1");

To commit your changes to the database (when "AutoCommit" is off):

        $dbh->commit;  # or call $dbh->rollback; to undo changes

Finally, when you have finished working with the data source, you should "disconnect" from it:

        $dbh->disconnect;

General Interface Rules & Caveats

The DBI does not have a concept of a "current session". Every session has a handle object (i.e., a $dbh) returned from the "connect" method. That handle object is used to invoke database related methods.

Most data is returned to the Perl script as strings. (Null values are returned as "undef".) This allows arbitrary precision numeric data to be handled without loss of accuracy. Beware that Perl may not preserve the same accuracy when the string is used as a number.

Dates and times are returned as character strings in the current default format of the corresponding database engine. Time zone effects are database/driver dependent.

Perl supports binary data in Perl strings, and the DBI will pass binary data to and from the driver without change. It is up to the driver implementors to decide how they wish to handle such binary data.

Most databases that understand multiple character sets have a default global charset. Text stored in the database is, or should be, stored in that charset; if not, then that's the fault of either the database or the application that inserted the data. When text is fetched it should be automatically converted to the charset of the client, presumably based on the locale. If a driver needs to set a flag to get that behaviour, then it should do so; it should not require the application to do that.

Multiple SQL statements may not be combined in a single statement handle ($sth), although some databases and drivers do support this (notably Sybase and SQL Server).

Non-sequential record reads are not supported in this version of the DBI. In other words, records can only be fetched in the order that the database returned them, and once fetched they are forgotten.

Positioned updates and deletes are not directly supported by the DBI. See the description of the "CursorName" attribute for an alternative.

Individual driver implementors are free to provide any private 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 modules 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 signify who defined the meaning of that name and its values.

        Case of name  Has a meaning defined by
        ------------  ------------------------
        UPPER_CASE    Standards, e.g.,  X/Open, ISO SQL92 etc (portable)
        MixedCase     DBI API (portable), underscores are not used.
        lower_case    Driver or database engine specific (non-portable)

It is of the utmost importance that Driver developers only use lower case attribute names when defining private attributes. Private attribute names must be prefixed with the driver name or suitable abbreviation (e.g., ""ora_"" for Oracle, ""ing_"" for Ingres, etc).

SQL - A Query Language

Most DBI drivers require applications to use a dialect of SQL (Structured Query Language) to interact with the database engine. The "Standards Reference Information" section provides links to useful information about SQL.

The DBI itself does not mandate or require any particular language to be used; it is language independent. In ODBC terms, the DBI is in "pass-thru" mode, although individual drivers might not be. The only requirement is that queries and other statements must be expressed as a single string of characters passed as the first argument to the "prepare" or "do" methods.

For an interesting diversion on the real history of RDBMS and SQL, from the people who made it happen, see:

        http://ftp.digital.com/pub/DEC/SRC/technical-notes/SRC-1997-018-html/sqlr95.html

Follow the "Full Contents" then "Intergalactic dataspeak" links for the SQL history.

Placeholders and Bind Values

Some drivers support placeholders and bind values. Placeholders, also called parameter markers, are used to indicate values in a database statement that will be supplied later, before the prepared statement is executed. For example, an application might use the following to insert a row of data into the SALES table:

        INSERT INTO sales (product_code, qty, price) VALUES (?, ?, ?)

or the following, to select the description for a product:

        SELECT description FROM products WHERE product_code = ?

The "?" characters are the placeholders. The association of actual values with placeholders is known as binding, and the values are referred to as bind values.

Note that the "?" is not enclosed in quotation marks, even when the placeholder represents a string. Some drivers also allow placeholders like ":"name and ":"n (e.g., ":1", ":2", and so on) in addition to "?", but their use is not portable.

With most drivers, placeholders can't be used for any element of a statement that would prevent the database server from validating the statement and creating a query execution plan for it. For example:

        "SELECT name, age FROM ?"         # wrong (will probably fail)
        "SELECT name, ?   FROM people"    # wrong (but may not 'fail')

Also, placeholders can only represent single scalar values. For example, the following statement won't work as expected for more than one value:

        "SELECT name, age FROM people WHERE name IN (?)"    # wrong
        "SELECT name, age FROM people WHERE name IN (?,?)"  # two names

When using placeholders with the SQL "LIKE" qualifier, you must 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. Sadly, that more general syntax doesn't work for Sybase and MS SQL Server. However on those two servers the original ""product_code = ?"" syntax works for binding nulls.

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 statement. Use the double-quote like "qq{...}" operator if you want to interpolate variables into the string. See "Quote and Quote-like Operators" in perlop for more details.

See also the "bind_columns" method, which is used to associate Perl variables with the output columns of a "SELECT" statement.

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 support that data type.

DBI Class Methods

The following methods are provided by the DBI class:

"parse_dsn"
            ($scheme, $driver, $attr_string, $attr_hash, $driver_dsn) = DBI->parse_dsn($dsn)
                or die "Can't parse DBI DSN '$dsn'";

Breaks apart a DBI Data Source Name (DSN) and returns the individual parts. If $dsn doesn't contain a valid DSN then parse_dsn() returns an empty list.

$scheme is the first part of the DSN and is currently always 'dbi'. $driver is the driver name, possibly defaulted to $ENV{DBI_DRIVER}, and may be undefined. $attr_string is the optional attribute string, which may be undefined. If $attr_string is true then $attr_hash is a reference to a hash containing the parsed attribute names and values. $driver_dsn is the last part of the DBI DSN string.

The parse_dsn() method was added in DBI 1.43.

="connect"

            $dbh = DBI->connect($data_source, $username, $password)
                      or die $DBI::errstr;
            $dbh = DBI->connect($data_source, $username, $password, \%attr)
                      or die $DBI::errstr;

Establishes a database connection, or session, to the requested $data_source. Returns a database handle object if the connection succeeds. Use "$dbh->disconnect" to terminate the connection.

If the connect fails (see below), it returns "undef" and sets both $DBI::err and $DBI::errstr. (It does not explicitly set $!.) You should generally test the return status of "connect" and "print $DBI::errstr" if it has failed.

Multiple simultaneous connections to multiple databases through multiple drivers can be made via the DBI. Simply make one "connect" call for each database and keep a copy of each returned database handle.

The $data_source value must begin with ""dbi:"driver_name":"". The driver_name specifies the driver that will be used to make the connection. (Letter case is significant.)

As a convenience, if the $data_source parameter is undefined or empty, the DBI will substitute the value of the environment variable "DBI_DSN". If just the driver_name part is empty (i.e., the $data_source prefix is ""dbi::""), the environment variable "DBI_DRIVER" is used. If neither variable is set, then "connect" dies.

Examples of $data_source values are:

            dbi:DriverName:database_name
            dbi:DriverName:database_name@hostname:port
            dbi:DriverName:database=database_name;host=hostname;port=port

There is no standard for the text following the driver name. Each driver is free to use whatever syntax it wants. The only 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:

            $ENV{DBI_AUTOPROXY};dsn=$data_source

"DBI_AUTOPROXY" is typically set as ""dbi:Proxy:hostname=...;port=..."". If $ENV{DBI_AUTOPROXY} doesn't begin with '"dbi:"' then "dbi:Proxy:" will be prepended to it first. See the DBD::Proxy documentation for more details.

If $username or $password are undefined (rather than just empty), then the DBI will substitute the values of the "DBI_USER" and "DBI_PASS" environment variables, respectively. The DBI will warn if the environment variables are not defined. However, the everyday use of these environment variables is not recommended for security reasons. The mechanism is primarily intended to simplify testing. See below for alternative way to specify the username and password.

"DBI->connect" automatically installs the driver if it has not been installed yet. Driver installation either returns a valid driver handle, or it dies with an error message that includes the string ""install_driver"" and the underlying problem. So "DBI->connect" will die on a driver installation failure and will only return "undef" on a connect failure, in which case $DBI::errstr will hold the error message. Use "eval { ... }" if you need to catch the ""install_driver"" error.

The $data_source argument (with the ""dbi:...:"" prefix removed) and the $username and $password arguments are then passed to the driver for processing. The DBI does not define any interpretation for the contents of these fields. The driver is free to interpret the $data_source, $username, and $password fields in any way, and supply whatever defaults are appropriate for the engine being accessed. (Oracle, for example, uses the ORACLE_SID and TWO_TASK environment variables if no $data_source is specified.)

The "AutoCommit" and "PrintError" attributes for each connection default to "on". (See "AutoCommit" and "PrintError" for more information.) However, it is strongly recommended that you explicitly define "AutoCommit" rather than rely on the default. The "PrintWarn" attribute defaults to on if $^W is true, i.e., perl is running with warnings enabled.

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

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

The username and password can also be specified using the attributes "Username" and "Password", in which case they take precedence over the $username and $password parameters.

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

            dbi:DriverName(PrintWarn=>1,PrintError=>0,Taint=>1):...

Individual attributes values specified in this way take precedence over any conflicting values specified via the "\%attr" parameter to "connect".

The "dbi_connect_method" attribute can be used to specify which driver method should be called to establish the connection. The only useful values are 'connect', 'connect_cached', or some 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 useful when you need to hold cursors open across transactions--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 argument to "connect" (instead of "\%attr"):

            $dbh = DBI->connect($data_source, $user, $pass, $driver);

In this "old-style" form of "connect", the $data_source should not start with ""dbi:driver_name:"". (If it does, the embedded driver_name will be ignored). Also note that in this older form of "connect", the "$dbh->{AutoCommit}" attribute is undefined, the "$dbh->{PrintError}" attribute is off, and the old "DBI_DBNAME" environment variable is checked if "DBI_DSN" is not defined. Beware that this "old-style" "connect" will soon be withdrawn in a future version of DBI.

"connect_cached"
            $dbh = DBI->connect_cached($data_source, $username, $password)
                      or die $DBI::errstr;
            $dbh = DBI->connect_cached($data_source, $username, $password, \%attr)
                      or die $DBI::errstr;

"connect_cached" is like "connect", except that the database handle returned is also stored in a hash associated with the given 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 behaviour of this method differs in several respects from the behaviour of persistent connections implemented by Apache::DBI.

Caching connections can be useful in some applications, but it can also cause problems, such as too many connections, and so should be used with care.

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 directories. Passing a true value for $quiet will inhibit the warning.

      "installed_versions"
            DBI->installed_versions;
            @ary  = DBI->installed_versions;
            %hash = DBI->installed_versions;
          Calls available_drivers() and attempts to load each of them in turn
          using install_driver().  For each load that succeeds the driver
          name and version number are added to a hash. When running under
          DBI::PurePerl drivers which appear not be pure-perl are ignored.
          When called in array context the list of successfully loaded
          drivers is returned (without the 'DBD::' prefix).
          When called in scalar context a reference to the hash is returned
          and the hash will also contain other entries for the "DBI" version,
          "OS" name, etc.
          When called in a void context the installed_versions() method will
          print out a formatted list of the hash contents, one per line.
          Due to the potentially high memory cost and unknown risks of load-
          ing in an unknown number of drivers that just happen to be
          installed on the system, this method is nor recommended for general
          use.  Use available_drivers() instead.
          The installed_versions() method is primarily intended as a quick
          way to see from the command line what's installed. For example:
            perl -MDBI -e 'DBI->installed_versions'
          The installed_versions() method was added in DBI 1.38.
      "data_sources"
            @ary = DBI->data_sources($driver);
            @ary = DBI->data_sources($driver, \%attr);
          Returns a list of data sources (databases) available via the named
          driver.  If $driver is empty or "undef", then the value of the
          "DBI_DRIVER" environment variable is used.
          The driver will be loaded if it hasn't been already. Note that if
          the driver loading fails then data_sources() dies with an error
          message that includes the string ""install_driver"" and the under-
          lying problem.
          Data sources are returned in a form suitable for passing to the
          "connect" method (that is, they will include the ""dbi:$driver:""
          prefix).
          Note that many drivers have no way of knowing what data sources
          might be available for it. These drivers return an empty or incom-
          plete list or may require driver-specific attributes.
          There is also a data_sources() method defined for database handles.
      "trace"
            DBI->trace($trace_setting)
            DBI->trace($trace_setting, $trace_filename)
            $trace_setting = DBI->trace;
          The "DBI->trace" method sets the global default trace settings and
          returns the previous trace settings. It can also be used to change
          where the trace output is sent.
          There's a similar method, "$h->trace", which sets the trace set-
          tings for the specific handle it's called on.
          See the "TRACING" section for full details about the DBI's powerful
          tracing facilities.
      DBI Utility Functions
      In addition to the DBI methods listed in the previous section, the DBI
      package also provides several utility functions.
      These can be imported into your code by listing them in the "use"
      statement. For example:
        use DBI qw(neat data_diff);
      Alternatively, all these utility functions (except hash) can be
      imported using the ":utils" import tag. For example:
        use DBI qw(:utils);
      "data_string_desc"
            $description = data_string_desc($string);
          Returns an informal description of the string. For example:
            UTF8 off, ASCII, 42 characters 42 bytes
            UTF8 off, non-ASCII, 42 characters 42 bytes
            UTF8 on, non-ASCII, 4 characters 6 bytes
            UTF8 on but INVALID encoding, non-ASCII, 4 characters 6 bytes
            UTF8 off, undef
          The initial "UTF8" on/off refers to Perl's internal SvUTF8 flag.
          If $string has the SvUTF8 flag set but the sequence of bytes it
          contains are not a valid UTF-8 encoding then data_string_desc()
          will report "UTF8 on but INVALID encoding".
          The "ASCII" vs "non-ASCII" portion shows "ASCII" if all the charac-
          ters in the string are ASCII (have code points <= 127).
          The data_string_desc() function was added in DBI 1.46.
      "data_string_diff"
            $diff = data_string_diff($a, $b);
          Returns an informal description of the first character difference
          between the strings. If both $a and $b contain the same sequence of
          characters then data_string_diff() returns an empty string.  For
          example:
           Params a & b     Result
           ------------     ------
           'aaa', 'aaa'     
           'aaa', 'abc'     'Strings differ at index 2: a[2]=a, b[2]=b'
           'aaa', undef     'String b is undef, string a has 3 characters'
           'aaa', 'aa'      'String b truncated after 2 characters'
          Unicode characters are reported in "\x{XXXX}" format. Unicode code
          points in the range U+0800 to U+08FF are unassigned and most likely
          to occur due to double-encoding. Characters in this range are
          reported as "\x{08XX}='C'" where "C" is the corresponding latin-1
          character.
          The data_string_diff() function only considers logical characters
          and not the underlying encoding. See "data_diff" for an alterna-
          tive.
          The data_string_diff() function was added in DBI 1.46.
      "data_diff"
            $diff = data_diff($a, $b);
            $diff = data_diff($a, $b, $logical);
          Returns an informal description of the difference between two
          strings.  It calls "data_string_desc" and "data_string_diff" and
          returns the combined results as a multi-line string.
          For example, "data_diff("abc", "ab\x{263a}")" will return:
            a: UTF8 off, ASCII, 3 characters 3 bytes
            b: UTF8 on, non-ASCII, 3 characters 5 bytes
            Strings differ at index 2: a[2]=c, b[2]=\x{263A}
          If $a and $b are identical in both the characters they contain and
          their physical encoding then data_diff() returns an empty string.
          If $logical is true then physical encoding differences are ignored
          (but are still reported if there is a difference in the charac-
          ters).
          The data_diff() function was added in DBI 1.46.
      "neat"
            $str = neat($value);
            $str = neat($value, $maxlen);
          Return a string containing a neat (and tidy) representation of the
          supplied value.
          Strings will be quoted, although internal quotes will not be
          escaped.  Values known to be numeric will be unquoted. Undefined
          (NULL) values will be shown as "undef" (without quotes).
          If the string is flagged internally as utf8 then double quotes will
          be used, otherwise single quotes are used and unprintable charac-
          ters will be replaced by dot (.).
          For result strings longer than $maxlen the result string will be
          truncated to "$maxlen-4" and ""...'"" will be appended.  If $maxlen
          is 0 or "undef", it defaults to $DBI::neat_maxlen which, in turn,
          defaults to 400.
          This function is designed to format values for human consumption.
          It is used internally by the DBI for "trace" output. It should typ-
          ically not be used for formatting values for database use.  (See
          also "quote".)
      "neat_list"
            $str = neat_list(\@listref, $maxlen, $field_sep);
          Calls "neat" on each element of the list and returns a string con-
          taining the results joined with $field_sep. $field_sep defaults to
          ", ".
      "looks_like_number"
            @bool = looks_like_number(@array);
          Returns true for each element that looks like a number.  Returns
          false for each element that does not look like a number.  Returns
          "undef" for each element that is undefined or empty.
      "hash"
            $hash_value = DBI::hash($buffer, $type);
          Return a 32-bit integer 'hash' value corresponding to the contents
          of $buffer.  The $type parameter selects which kind of hash algo-
          rithm should be used.
          For the technically curious, type 0 (which is the default if $type
          isn't specified) is based on the Perl 5.1 hash except that the
          value is forced to be negative (for obscure historical reasons).
          Type 1 is the better "Fowler / Noll / Vo" (FNV) hash. See
          <http://www.isthe.com/chongo/tech/comp/fnv/> for more information.
          Both types are implemented in C and are very fast.
          This function doesn't have much to do with databases, except that
          it can be handy to store hash values in a database.
      DBI Dynamic Attributes
      Dynamic attributes are always associated with the last handle used
      (that handle is represented by $h in the descriptions below).
      Where an attribute is equivalent to a method call, then refer to the
      method call for all related documentation.
      Warning: these attributes are provided as a convenience but they do
      have limitations. Specifically, they have a short lifespan: because
      they are associated with the last handle used, they should only be used
      immediately after calling the method that "sets" them.  If in any
      doubt, use the corresponding method call.
      $DBI::err
          Equivalent to "$h->err".
      $DBI::errstr
          Equivalent to "$h->errstr".
      $DBI::state
          Equivalent to "$h->state".
      $DBI::rows
          Equivalent to "$h->rows". Please refer to the documentation for the
          "rows" method.
      $DBI::lasth
          Returns the DBI object handle used for the most recent DBI method
          call.  If the last DBI method call was a DESTROY then $DBI::lasth
          will return the handle of the parent of the destroyed handle, if
          there is one.

METHODS COMMON TO ALL HANDLES

      The following methods can be used by all types of DBI handles.
      "err"
            $rv = $h->err;
          Returns the native database engine error code from the last driver
          method called. The code is typically an integer but you should not
          assume that.
          The DBI resets $h->err to undef before most DBI method calls, so
          the value only has a short lifespan. Also, for most drivers, the
          statement handles share the same error variable as the parent
          database handle, so calling a method on one handle may reset the
          error on the related handles.
          If you need to test for individual errors and have your program be
          portable to different database engines, then you'll need to deter-
          mine what the corresponding error codes are for all those engines
          and test for all of them.
          A driver may return 0 from err() to indicate a warning condition
          after a method call. Similarly, a driver may return an empty string
          to indicate a 'success with information' condition. In both these
          cases the value is false but not undef. The errstr() and state()
          methods may be used to retrieve extra information in these cases.
          See "set_err" for more information.
      "errstr"
            $str = $h->errstr;
          Returns the native database engine error message from the last DBI
          method called. This has the same lifespan issues as the "err"
          method described above.
          The returned string may contain multiple messages separated by new-
          line characters.
          The errstr() method should not be used to test for errors, use
          err() for that, because drivers may return 'success with informa-
          tion' or warning messages via errstr() for methods that have not
          'failed'.
          See "set_err" for more information.
      "state"
            $str = $h->state;
          Returns a state code in the standard SQLSTATE five character for-
          mat.  Note that the specific success code 00000 is translated to
          any empty string (false). If the driver does not support SQLSTATE
          (and most don't), then state will return "S1000" (General Error)
          for all errors.
          The driver is free to return any value via "state", e.g., warning
          codes, even if it has not declared an error by returning a true
          value via the "err" method described above.
          The state() method should not be used to test for errors, use err()
          for that, because drivers may return a 'success with information'
          or warning state code via errstr() for methods that have not
          'failed'.
      "set_err"
            $rv = $h->set_err($err, $errstr);
            $rv = $h->set_err($err, $errstr, $state);
            $rv = $h->set_err($err, $errstr, $state, $method);
            $rv = $h->set_err($err, $errstr, $state, $method, $rv);
          Set the "err", "errstr", and "state" values for the handle.  This
          method is typically only used by DBI drivers and DBI subclasses.
          If the "HandleSetErr" attribute holds a reference to a subroutine
          it is called first. The subroutine can alter the $err, $errstr,
          $state, and $method values. See "HandleSetErr" for full details.
          If the subroutine returns a true value then the handle "err",
          "errstr", and "state" values are not altered and set_err() returns
          an empty list (it normally returns $rv which defaults to undef, see
          below).
          Setting "err" to a true value indicates an error and will trigger
          the normal DBI error handling mechanisms, such as "RaiseError" and
          "HandleError", if they are enabled, when execution returns from the
          DBI back to the application.
          Setting "err" to "" indicates an 'information' state, and setting
          it to "0" indicates a 'warning' state. Setting "err" to "undef"
          also sets "errstr" to undef, and "state" to "", irrespective of the
          values of the $errstr and $state parameters.
          The $method parameter provides an alternate method name for the
          "RaiseError"/"PrintError"/"PrintWarn" error string instead of the
          fairly unhelpful '"set_err"'.
          The "set_err" method normally returns undef.  The $rv parameter
          provides an alternate return value.
          Some special rules apply if the "err" or "errstr" values for the
          handle are already set...
          If "errstr" is true then: "" [err was %s now %s]"" is appended if
          $err is true and "err" is already true; "" [state was %s now %s]""
          is appended if $state is true and "state" is already true; then
          ""\n"" and the new $errstr are appended. Obviously the %s's above
          are replaced by the corresponding values.
          The handle "err" value is set to $err if: $err is true; or handle
          "err" value is undef; or $err is defined and the length is greater
          than the handle "err" length. The effect is that an 'information'
          state only overrides undef; a 'warning' overrides undef or 'infor-
          mation', and an 'error' state overrides anything.
          The handle "state" value is set to $state if $state is true and the
          handle "err" value was set (by the rules above).
          Support for warning and information states was added in DBI 1.41.
      "trace"
            $h->trace($trace_settings);
            $h->trace($trace_settings, $trace_filename);
            $trace_settings = $h->trace;
          The trace() method is used to alter the trace settings for a handle
          (and any future children of that handle).  It can also be used to
          change where the trace output is sent.
          There's a similar method, "DBI->trace", which sets the global
          default trace settings.
          See the "TRACING" section for full details about the DBI's powerful
          tracing facilities.
      "trace_msg"
            $h->trace_msg($message_text);
            $h->trace_msg($message_text, $min_level);
          Writes $message_text to the trace file if the trace level is
          greater than or equal to $min_level (which defaults to 1).  Can
          also be called as "DBI->trace_msg($msg)".
          See "TRACING" for more details.
      "func"
            $h->func(@func_arguments, $func_name) or die ...;
          The "func" method can be used to call private non-standard and non-
          portable methods implemented by the driver. Note that the function
          name is given as the last argument.
          It's also important to note that the func() method does not clear a
          previous error ($DBI::err etc.) and it does not trigger automatic
          error detection (RaiseError etc.) so you must check the return sta-
          tus and/or $h->err to detect errors.
          (This method is not directly related to calling stored procedures.
          Calling stored procedures is currently not defined by the DBI.
          Some drivers, such as DBD::Oracle, support it in non-portable ways.
          See driver documentation for more details.)
          See also "install_method" for how you can avoid needing to use
          func() and gain.
      "can"
            $is_implemented = $h->can($method_name);
          Returns true if $method_name is implemented by the driver or a
          default method is provided by the DBI.  It returns false where a
          driver hasn't implemented a method and the default method is pro-
          vided by the DBI is just an empty stub.
      "parse_trace_flags"
            $trace_settings_integer = $h->parse_trace_flags($trace_settings);
          Parses a string containing trace settings and returns the corre-
          sponding integer value used internally by the DBI and drivers.
          The $trace_settings argument is a string containing a trace level
          between 0 and 15 and/or trace flag names separated by vertical bar
          (""|"") or comma ("","") characters. For example: "SQL|3|foo".
          It uses the parse_trace_flag() method, described below, to process
          the individual trage flag names.
          The parse_trace_flags() method was added in DBI 1.42.
      "parse_trace_flag"
            $bit_flag = $h->parse_trace_flag($trace_flag_name);
          Returns the bit flag corresponding to the trace flag name in
          $trace_flag_name.  Drivers are expected to override this method and
          check if $trace_flag_name is a driver specific trace flags and, if
          not, then call the DBIs default parse_trace_flag().
          The parse_trace_flag() method was added in DBI 1.42.
      "swap_inner_handle"
            $rc = $h1->swap_inner_handle( $h2 );
            $rc = $h1->swap_inner_handle( $h2, $allow_reparent );
          Brain transplants for handles. You don't need to know about this
          unless you want to become a handle surgeon.
          A DBI handle is a reference to a tied hash. A tied hash has an
          inner hash that actually holds the contents.  The swap_inner_han-
          dle() method swaps the inner hashes between two handles. The $h1
          and $h2 handles still point to the same tied hashes, but what those
          hashes are tied to has been swapped.  In effect $h1 becomes $h2 and
          vice-versa. This is powerful stuff. Use with care.
          As a small safety measure, the two handles, $h1 and $h2, have to
          share the same parent unless $allow_reparent is true.
          The swap_inner_handle() method was added in DBI 1.44.

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 statement handle do not affect the parent database handle and
      changes to the database handle do not affect existing statement han-
      dles, only future ones.
      Attempting to set or get the value of an unknown attribute generates a
      warning, except for private driver specific attributes (which all have
      names starting with a lowercase letter).
      Example:
        $h->{AttributeName} = ...;    # set/write
        ... = $h->{AttributeName};    # get/read
      "Warn" (boolean, inherited)
          The "Warn" attribute enables useful warnings for certain bad prac-
          tices. It is enabled by default and should only be disabled in rare
          circumstances.  Since warnings are generated using the Perl "warn"
          function, they can be intercepted using the Perl $SIG{__WARN__}
          hook.
          The "Warn" attribute is not related to the "PrintWarn" attribute.
      "Active" (boolean, read-only)
          The "Active" attribute is true if the handle object is "active".
          This is rarely used in applications. The exact meaning of active is
          somewhat vague at the moment. For a database handle it typically
          means that the handle is connected to a database ("$dbh->discon-
          nect" sets "Active" off).  For a statement handle it typically
          means that the handle is a "SELECT" that may have more data to
          fetch. (Fetching all the data or calling "$sth->finish" sets
          "Active" off.)
      "Executed" (boolean)
          The "Executed" attribute is true if the handle object has been
          "executed".  Currently only the $dbh do() method and the $sth exe-
          cute(), execute_array(), and execute_for_fetch() methods set the
          "Executed" attribute.
          When it's set on a handle it is also set on the parent handle at
          the same time. So calling execute() on a $sth also sets the "Exe-
          cuted" attribute on the parent $dbh.
          The "Executed" attribute for a database handle is cleared by the
          commit() and rollback() methods. The "Executed" attribute of a
          statement handle is not cleared by the DBI under any circumstances
          and so acts as a permanent record of whether the statement handle
          was ever used.
          The "Executed" attribute was added in DBI 1.41.
      "Kids" (integer, read-only)
          For a driver handle, "Kids" is the number of currently existing
          database handles that were created from that driver handle.  For a
          database handle, "Kids" is the number of currently existing state-
          ment handles that were created from that database handle.  For a
          statement handle, the value is zero.
      "ActiveKids" (integer, read-only)
          Like "Kids", but only counting those that are "Active" (as above).
      "CachedKids" (hash ref)
          For a database handle, "CachedKids" returns a reference to the
          cache (hash) of statement handles created by the "prepare_cached"
          method.  For a driver handle, returns a reference to the cache
          (hash) of database handles created by the "connect_cached" method.
      "CompatMode" (boolean, inherited)
          The "CompatMode" attribute is used by emulation layers (such as
          Oraperl) to enable compatible behaviour in the underlying driver
          (e.g., DBD::Oracle) for this handle. Not normally set by applica-
          tion code.
          It also has the effect of disabling the 'quick FETCH' of attribute
          values from the handles attribute cache. So all attribute values
          are handled by the drivers own FETCH method. This makes them
          slightly slower but is useful for special-purpose drivers like
          DBD::Multiplex.
      "InactiveDestroy" (boolean)
          The "InactiveDestroy" attribute can be used to disable the database
          engine related effect of DESTROYing a handle (which would normally
          close a prepared statement or disconnect from the database etc).
          The default value, false, means a handle will be fully destroyed
          when it passes out of scope.
          For a database handle, this attribute does not disable an explicit
          call to the disconnect method, only the implicit call from DESTROY
          that happens if the handle is still marked as "Active".
          Think of the name as meaning 'treat the handle as not-Active in the
          DESTROY method'.
          This attribute is specifically designed for use in Unix applica-
          tions that "fork" child processes. Either the parent or the child
          process, but not both, should set "InactiveDestroy" on all their
          shared handles.  Note that some databases, including Oracle, don't
          support passing a database connection across a fork.
          To help tracing applications using fork the process id is shown in
          the trace log whenever a DBI or handle trace() method is called.
          The process id also shown for every method call if the DBI trace
          level (not handle trace level) is set high enough to show the trace
          from the DBI's method dispatcher, e.g. >= 9.
      "PrintWarn" (boolean, inherited)
          The "PrintWarn" attribute controls the printing of warnings
          recorded by the driver.  When set to a true value the DBI will
          check method calls to see if a warning condition has been set. If
          so, the DBI will effectively do a "warn("$class $method warning:
          $DBI::errstr")" where $class is the driver class and $method is the
          name of the method which failed. E.g.,
            DBD::Oracle::db execute warning: ... warning text here ...
          By default, "DBI->connect" sets "PrintWarn" "on" if $^W is true,
          i.e., perl is running with warnings enabled.
          If desired, the warnings can be caught and processed using a
          $SIG{__WARN__} handler or modules like CGI::Carp and CGI::Error-
          Wrap.
          See also "set_err" for how warnings are recorded and "HandleSetErr"
          for how to influence it.
          Fetching the full details of warnings can require an extra round-
          trip to the database server for some drivers. In which case the
          driver may opt to only fetch the full details of warnings if the
          "PrintWarn" attribute is true. If "PrintWarn" is false then these
          drivers should still indicate the fact that there were warnings by
          setting the warning string to, for example: "3 warnings".
      "PrintError" (boolean, inherited)
          The "PrintError" attribute can be used to force errors to generate
          warnings (using "warn") in addition to returning error codes in the
          normal way.  When set "on", any method which results in an error
          occuring will cause the DBI to effectively do a "warn("$class
          $method failed: $DBI::errstr")" where $class is the driver class
          and $method is the name of the method which failed. E.g.,
            DBD::Oracle::db prepare failed: ... error text here ...
          By default, "DBI->connect" sets "PrintError" "on".
          If desired, the warnings can be caught and processed using a
          $SIG{__WARN__} handler or modules like CGI::Carp and CGI::Error-
          Wrap.
      "RaiseError" (boolean, inherited)
          The "RaiseError" attribute can be used to force errors to raise
          exceptions rather than simply return error codes in the normal way.
          It is "off" by default.  When set "on", any method which results in
          an error will cause the DBI to effectively do a "die("$class
          $method failed: $DBI::errstr")", where $class is the driver class
          and $method is the name of the method that failed. E.g.,
            DBD::Oracle::db prepare failed: ... error text here ...
          If you turn "RaiseError" on then you'd normally turn "PrintError"
          off.  If "PrintError" is also on, then the "PrintError" is done
          first (naturally).
          Typically "RaiseError" is used in conjunction with "eval { ... }"
          to catch the exception that's been thrown and followed by an "if
          ($@) { ... }" block to handle the caught exception. 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".
      "HandleError" (code ref, inherited)
          The "HandleError" attribute can be used to provide your own alter-
          native behaviour in case of errors. If set to a reference to a sub-
          routine then that subroutine is called when an error is detected
          (at the same point that "RaiseError" and "PrintError" are handled).
          The subroutine is called with three parameters: the error message
          string that "RaiseError" and "PrintError" would use, the DBI handle
          being used, and the first value being returned by the method that
          failed (typically undef).
          If the subroutine returns a false value then the "RaiseError"
          and/or "PrintError" attributes are checked and acted upon as nor-
          mal.
          For example, to "die" with a full stack trace for any error:
            use Carp;
            $h->{HandleError} = sub { confess(shift) };
          Or to turn errors into exceptions:
            use Exception; # or your own favourite exception module
            $h->{HandleError} = sub { Exception->new('DBI')->raise($_[0]) };
          It is possible to 'stack' multiple HandleError handlers by using
          closures:
            sub your_subroutine {
              my $previous_handler = $h->{HandleError};
              $h->{HandleError} = sub {
                return 1 if $previous_handler and &$previous_handler(@_);
                ... your code here ...
              };
            }
          Using a "my" inside a subroutine to store the previous "HandleEr-
          ror" value is important.  See perlsub and perlref for more informa-
          tion about closures.
          It is possible for "HandleError" to alter the error message that
          will be used by "RaiseError" and "PrintError" if it returns false.
          It can do that by altering the value of $_[0]. This example appends
          a stack trace to all errors and, unlike the previous example using
          Carp::confess, this will work "PrintError" as well as "RaiseError":
            $h->{HandleError} = sub { $_[0]=Carp::longmess($_[0]); 0; };
          It is also possible for "HandleError" to hide an error, to a lim-
          ited degree, by using "set_err" to reset $DBI::err and
          $DBI::errstr, and altering the return value of the failed method.
          For example:
            $h->{HandleError} = sub {
              return 0 unless $_[0] =~ /^\S+ fetchrow_arrayref failed:/;
              return 0 unless $_[1]->err == 1234; # the error to 'hide'
              $h->set_err(undef,undef);   # turn off the error
              $_[2] = [ ... ];    # supply alternative return value
              return 1;
            };
          This only works for methods which return a single value and is hard
          to make reliable (avoiding infinite loops, for example) and so
          isn't recommended for general use!  If you find a good use for it
          then please let me know.
      "HandleSetErr" (code ref, inherited)
          The "HandleSetErr" attribute can be used to intercept the setting
          of handle "err", "errstr", and "state" values.  If set to a refer-
          ence to a subroutine then that subroutine is called whenever
          set_err() is called, typically by the driver or a subclass.
          The subroutine is called with five arguments, the first five that
          were passed to set_err(): the handle, the "err", "errstr", and
          "state" values being set, and the method name. These can be altered
          by changing the values in the @_ array. The return value affects
          set_err() behaviour, see "set_err" for details.
          It is possible to 'stack' multiple HandleSetErr handlers by using
          closures. See "HandleError" for an example.
          The "HandleSetErr" and "HandleError" subroutines differ in subtle
          but significant ways. HandleError is only invoked at the point
          where the DBI is about to return to the application with "err" set
          true.  It's not invoked by the failure of a method that's been
          called by another DBI method.  HandleSetErr, on the other hand, is
          called whenever set_err() is called with a defined "err" value,
          even if false.  So it's not just for errors, despite the name, but
          also warn and info states.  The set_err() method, and thus Handle-
          SetErr, may be called multiple times within a method and is usually
          invoked from deep within driver code.
          In theory a driver can use the return value from HandleSetErr via
          set_err() to decide whether to continue or not. If set_err()
          returns an empty list, indicating that the HandleSetErr code has
          'handled' the 'error', the driver could then continue instead of
          failing (if that's a reasonable thing to do).  This isn't excepted
          to be common and any such cases should be clearly marked in the
          driver documentation and discussed on the dbi-dev mailing list.
          The "HandleSetErr" attribute was added in DBI 1.41.
      "ErrCount" (unsigned integer)
          The "ErrCount" attribute is incremented whenever the set_err()
          method records an error. It isn't incremented by warnings or infor-
          mation states. It is not reset by the DBI at any time.
          The "ErrCount" attribute was added in DBI 1.41. Older drivers may
          not have been updated to use set_err() to record errors and so this
          attribute may not be incremented when using them.
      "ShowErrorStatement" (boolean, inherited)
          The "ShowErrorStatement" attribute can be used to cause the rele-
          vant Statement text to be appended to the error messages generated
          by the "RaiseError", "PrintError", and "PrintWarn" attributes.
          Only applies to errors on statement handles plus the prepare(),
          do(), and the various "select*()" database handle methods.  (The
          exact format of the appended text is subject to change.)
          If "$h->{ParamValues}" returns a hash reference of parameter
          (placeholder) values then those are formatted and appended to the
          end of the Statement text in the error message.
      "TraceLevel" (integer, inherited)
          The "TraceLevel" attribute can be used as an alternative to the
          "trace" method to set the DBI trace level and trace flags for a
          specific handle.  See "TRACING" for more details.
          The "TraceLevel" attribute is especially useful combined with
          "local" to alter the trace settings for just a single block of
          code.
      "FetchHashKeyName" (string, inherited)
          The "FetchHashKeyName" attribute is used to specify whether the
          fetchrow_hashref() method should perform case conversion on the
          field names used for the hash keys. For historical reasons it
          defaults to '"NAME"' but it is recommended to set it to '"NAME_lc"'
          (convert to lower case) or '"NAME_uc"' (convert to upper case)
          according to your preference.  It can only be set for driver and
          database handles.  For statement handles the value is frozen when
          prepare() is called.
      "ChopBlanks" (boolean, inherited)
          The "ChopBlanks" attribute can be used to control the trimming of
          trailing space characters from fixed width character (CHAR) fields.
          No other field types are affected, even where field values have
          trailing spaces.
          The default is false (although it is possible that the default may
          change).  Applications that need specific behaviour should set the
          attribute as needed.
          Drivers are not required to support this attribute, but any driver
          which does not support it must arrange to return "undef" as the
          attribute value.
      "LongReadLen" (unsigned integer, inherited)
          The "LongReadLen" attribute may be used to control the maximum
          length of 'long' 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 dig-
          its.  For these types, "LongReadLen" relates to the underlying data
          length and not the doubled-up length of the encoded string.
          Changing the value of "LongReadLen" for a statement handle after it
          has been "prepare"'d will typically have no effect, so it's common
          to set "LongReadLen" on the $dbh before calling "prepare".
          For most drivers the value used here has a direct effect on the
          memory used by the statement handle while it's active, so don't be
          too generous. If you can't be sure what value to use you could exe-
          cute an extra select statement to determine the longest value.  For
          example:
            $dbh->{LongReadLen} = $dbh->selectrow_array{qq{
                SELECT MAX(long_column_name) FROM table WHERE ...
            });
            $sth = $dbh->prepare(qq{
                SELECT long_column_name, ... FROM table WHERE ...
            });
          You may need to take extra care if the table can be modified
          between the first select and the second being executed.
          See "LongTruncOk" for more information on truncation behaviour.
      "LongTruncOk" (boolean, inherited)
          The "LongTruncOk" attribute may be used to control the effect of
          fetching a long field value which has been truncated (typically
          because it's longer than the value of the "LongReadLen" attribute).
          By default, "LongTruncOk" is false and so fetching a long value
          that needs to be truncated will cause the fetch to fail.  (Applica-
          tions should always be sure to check for errors after a fetch loop
          in case an error, such as a divide by zero or long field trunca-
          tion, caused the fetch to terminate prematurely.)
          If a fetch fails due to a long field truncation when "LongTruncOk"
          is false, many drivers will allow you to continue fetching further
          rows.
          See also "LongReadLen".
      "TaintIn" (boolean, inherited)
          If the "TaintIn" attribute is set to a true value and Perl is run-
          ning in taint mode (e.g., started with the "-T" option), then all
          the arguments to most DBI method calls are checked for being
          tainted. This may change.
          The attribute defaults to off, even if Perl is in taint mode.  See
          perlsec for more about taint mode.  If Perl is not running in taint
          mode, this attribute has no effect.
          When fetching data that you trust you can turn off the TaintIn
          attribute, for that statement handle, for the duration of the fetch
          loop.
          The "TaintIn" attribute was added in DBI 1.31.
      "TaintOut" (boolean, inherited)
          If the "TaintOut" attribute is set to a true value and Perl is run-
          ning in taint mode (e.g., started with the "-T" option), then most
          data fetched from the database is considered tainted. This may
          change.
          The attribute defaults to off, even if Perl is in taint mode.  See
          perlsec for more about taint mode.  If Perl is not running in taint
          mode, this attribute has no effect.
          When fetching data that you trust you can turn off the TaintOut
          attribute, for that statement handle, for the duration of the fetch
          loop.
          Currently only fetched data is tainted. It is possible that the
          results of other DBI method calls, and the value of fetched
          attributes, may also be tainted in future versions. That change may
          well break your applications unless you take great care now. If you
          use DBI Taint mode, please report your experience and any sugges-
          tions for changes.
          The "TaintOut" attribute was added in DBI 1.31.
      "Taint" (boolean, inherited)
          The "Taint" attribute is a shortcut for "TaintIn" and "TaintOut"
          (it is also present for backwards compatibility).
          Setting this attribute sets both "TaintIn" and "TaintOut", and
          retrieving it returns a true value if and only if "TaintIn" and
          "TaintOut" are both set to true values.
      "Profile" (inherited)
          The "Profile" attribute enables the collection and reporting of
          method call timing statistics.  See the DBI::Profile module docu-
          mentation for much more detail.
          The "Profile" attribute was added in DBI 1.24.
      "private_your_module_name_*"
          The DBI provides a way to store extra information in a DBI handle
          as "private" attributes. The DBI will allow you to store and
          retrieve any attribute which has a name starting with ""private_"".
          It is strongly recommended that you use just one private attribute
          (e.g., use a hash ref) and give it a long and unambiguous name that
          includes the module or application name that the attribute relates
          to (e.g., ""private_YourFullModuleName_thingy"").
          Because of the way the Perl tie mechanism works you cannot reliably
          use the "||=" operator directly to initialise the attribute, like
          this:
            my $foo = $dbh->{private_yourmodname_foo} ||= { ... }; # WRONG
          you should use a two step approach like this:
            my $foo = $dbh->{private_yourmodname_foo};
            $foo ||= $dbh->{private_yourmodname_foo} = { ... };
          This attribute is primarily of interest to people sub-classing DBI.

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 handles:
      "clone"
            $new_dbh = $dbh->clone();
            $new_dbh = $dbh->clone(\%attr);
          The "clone" method duplicates the $dbh connection by connecting
          with the same parameters ($dsn, $user, $password) as originally
          used.
          The attributes for the cloned connect are the same as those used
          for the original connect, with some other attribute merged over
          them depending on the \%attr parameter.
          If \%attr is given then the attributes it contains are merged into
          the original attributes and override any with the same names.
          Effectively the same as doing:
            %attribues_used = ( %original_attributes, %attr );
          If \%attr is not given then it defaults to a hash containing all
          the attributes in the attribute cache of $dbh excluding any non-
          code references, plus the main boolean attributes (RaiseError,
          PrintError, AutoCommit, etc.). This behaviour is subject to change.
          The clone method can be used even if the database handle is discon-
          nected.
          The "clone" method was added in DBI 1.33. It is very new and likely
          to change.
      "data_sources"
            @ary = $dbh->data_sources();
            @ary = $dbh->data_sources(\%attr);
          Returns a list of data sources (databases) available via the $dbh
          driver's data_sources() method, plus any extra data sources that
          the driver can discover via the connected $dbh. Typically the extra
          data sources are other databases managed by the same server process
          that the $dbh is connected to.
          Data sources are returned in a form suitable for passing to the
          "connect" method (that is, they will include the ""dbi:$driver:""
          prefix).
          The data_sources() method, for a $dbh, was added in DBI 1.38.
      "do"
            $rows = $dbh->do($statement)           or die $dbh->errstr;
            $rows = $dbh->do($statement, \%attr)   or die $dbh->errstr;
            $rows = $dbh->do($statement, \%attr, @bind_values) or die ...
          Prepare and execute a single statement. Returns the number of rows
          affected or "undef" on error. A return value of "-1" means the num-
          ber of rows is not known, not applicable, or not available.
          This method is typically most useful for non-"SELECT" statements
          that either cannot be prepared in advance (due to a limitation of
          the driver) or do not need to be executed repeatedly. It should not
          be used for "SELECT" statements because it does not return a state-
          ment handle (so you can't fetch any data).
          The default "do" method is logically similar to:
            sub do {
                my($dbh, $statement, $attr, @bind_values) = @_;
                my $sth = $dbh->prepare($statement, $attr) or return undef;
                $sth->execute(@bind_values) or return undef;
                my $rows = $sth->rows;
                ($rows == 0) ? "0E0" : $rows; # always return true if no error
            }
          For example:
            my $rows_deleted = $dbh->do(q{
                DELETE FROM table
                WHERE status = ?
            }, undef, 'DONE') or die $dbh->errstr;
          Using placeholders and @bind_values with the "do" method can be
          useful because it avoids the need to correctly quote any variables
          in the $statement. But if you'll be executing the statement many
          times then it's more efficient to "prepare" it once and call "exe-
          cute" many times instead.
          The "q{...}" style quoting used in this example avoids clashing
          with quotes that may be used in the SQL statement. Use the double-
          quote-like "qq{...}" operator if you want to interpolate variables
          into the string.  See "Quote and Quote-like Operators" in perlop
          for more details.
      "last_insert_id"
            $rv = $dbh->last_insert_id($catalog, $schema, $table, $field);
            $rv = $dbh->last_insert_id($catalog, $schema, $table, $field, \%attr

);

          Returns a value 'identifying' the row just inserted, if possible.
          Typically this would be a value assigned by the database server to
          a column with an auto_increment or serial type.  Returns undef if
          the driver does not support the method or can't determine the
          value.
          The $catalog, $schema, $table, and $field parameters may be
          required for some drivers (see below).  If you don't know the
          parameter values and your driver does not need them, then use
          "undef" for each.
          There are several caveats to be aware of with this method if you
          want to use it for portable applications:
          * For some drivers the value may only available immediately after
          the insert statement has executed (e.g., mysql, Informix).
          * For some drivers the $catalog, $schema, $table, and $field param-
          eters are required (e.g., Pg), for others they are ignored (e.g.,
          mysql).
          * Drivers may return an indeterminate value if no insert has been
          performed yet.
          * For some drivers the value may only be available if placeholders
          have not been used (e.g., Sybase, MS SQL). In this case the value
          returned would be from the last non-placeholder insert statement.
          * Some drivers may need driver-specific hints about how to get the
          value. For example, being told the name of the database 'sequence'
          object that holds the value. Any such hints are passed as driver-
          specific attributes in the \%attr parameter.
          * If the underlying database offers nothing better, then some
          drivers may attempt to implement this method by executing ""select
          max($field) from $table"". Drivers using any approach like this
          should issue a warning if "AutoCommit" is true because it is gener-
          ally unsafe - another process may have modified the table between
          your insert and the select. For situations where you know it is
          safe, such as when you have locked the table, you can silence the
          warning by passing "Warn" => 0 in \%attr.
          * If no insert has been performed yet, or the last insert failed,
          then the value is implementation defined.
          Given all the caveats above, it's clear that this method must be
          used with care.
          The "last_insert_id" method was added in DBI 1.38.
      "selectrow_array"
            @row_ary = $dbh->selectrow_array($statement);
            @row_ary = $dbh->selectrow_array($statement, \%attr);
            @row_ary = $dbh->selectrow_array($statement, \%attr, @bind_values);
          This utility method combines "prepare", "execute" and
          "fetchrow_array" into a single call. If called in a list context,
          it returns the first row of data from the statement.  The $state-
          ment parameter can be a previously prepared statement handle, in
          which case the "prepare" is skipped.
          If any method fails, and "RaiseError" is not set, "selectrow_array"
          will return an empty list.
          If called in a scalar context for a statement handle that has more
          than one column, it is undefined whether the driver will return the
          value of the first column or the last. So don't do that.  Also, in
          a scalar context, an "undef" is returned if there are no more rows
          or if an error occurred. That "undef" can't be distinguished from
          an "undef" returned because the first field value was NULL.  For
          these reasons you should exercise some caution if you use "selec-
          trow_array" in a scalar context.
      "selectrow_arrayref"
            $ary_ref = $dbh->selectrow_arrayref($statement);
            $ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
            $ary_ref = $dbh->selectrow_arrayref($statement, \%attr, @bind_values);
          This utility method combines "prepare", "execute" and
          "fetchrow_arrayref" into a single call. It returns the first row of
          data from the statement.  The $statement parameter can be a
          previously prepared statement handle, in which case the "prepare"
          is skipped.
          If any method fails, and "RaiseError" is not set, "selectrow_array"
          will return undef.
      "selectrow_hashref"
            $hash_ref = $dbh->selectrow_hashref($statement);
            $hash_ref = $dbh->selectrow_hashref($statement, \%attr);
            $hash_ref = $dbh->selectrow_hashref($statement, \%attr, @bind_values);
          This utility method combines "prepare", "execute" and
          "fetchrow_hashref" into a single call. It returns the first row of
          data from the statement.  The $statement parameter can be a previ-
          ously prepared statement handle, in which case the "prepare" is
          skipped.
          If any method fails, and "RaiseError" is not set, "selec-
          trow_hashref" will return undef.
      "selectall_arrayref"
            $ary_ref = $dbh->selectall_arrayref($statement);
            $ary_ref = $dbh->selectall_arrayref($statement, \%attr);
            $ary_ref = $dbh->selectall_arrayref($statement, \%attr, @bind_values

);

          This utility method combines "prepare", "execute" and
          "fetchall_arrayref" into a single call. It returns a reference to
          an array containing a reference to an array for each row of data
          fetched.
          The $statement parameter can be a previously prepared statement
          handle, in which case the "prepare" is skipped. This is recommended
          if the statement is going to be executed many times.
          If "RaiseError" is not set and any method except
          "fetchall_arrayref" fails then "selectall_arrayref" will return
          "undef"; if "fetchall_arrayref" fails then it will return with
          whatever data has been fetched thus far. You should check
          "$sth->err" afterwards (or use the "RaiseError" attribute) to dis-
          cover if the data is complete or was truncated due to an error.
          The "fetchall_arrayref" method called by "selectall_arrayref" sup-
          ports a $max_rows parameter. You can specify a value for $max_rows
          by including a '"MaxRows"' attribute in \%attr. In which case fin-
          ish() is called for you after fetchall_arrayref() returns.
          The "fetchall_arrayref" method called by "selectall_arrayref" also
          supports a $slice parameter. You can specify a value for $slice by
          including a '"Slice"' or '"Columns"' attribute in \%attr. The only
          difference between the two is that if "Slice" is not defined and
          "Columns" is an array ref, then the array is assumed to contain
          column index values (which count from 1), rather than perl array
          index values.  In which case the array is copied and each value
          decremented before passing to "/fetchall_arrayref".
      "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 refer-
          ence to an array containing the values of the first column from
          each row.
          The $statement parameter can be a previously prepared statement
          handle, in which case the "prepare" is skipped. This is recommended
          if the statement is going to be executed many times.
          If any method except "fetch" fails, and "RaiseError" is not set,
          "selectcol_arrayref" will return "undef".  If "fetch" fails and
          "RaiseError" is not set, then it will return with whatever data it
          has fetched thus far. $DBI::err should be checked to catch that.
          The "selectcol_arrayref" method defaults to pushing a single column
          value (the first) from each row into the result array. However, it
          can also push another column, or even multiple columns per row,
          into the result array. This behaviour can be specified via a
          '"Columns"' attribute which must be a ref to an array containing
          the column number or numbers to use. For example:
            # get array of id and name pairs:
            my $ary_ref = $dbh->selectcol_arrayref("select id, name from table",
{ Columns=>[1,2] });
            my %hash = @$ary_ref; # build hash from key-value pairs so $hash{$id

} => name

          You can specify a maximum number of rows to fetch by including a
          '"MaxRows"' attribute in \%attr.
      "prepare"
            $sth = $dbh->prepare($statement)          or die $dbh->errstr;
            $sth = $dbh->prepare($statement, \%attr)  or die $dbh->errstr;
          Prepares a statement for later execution by the database engine and
          returns a reference to a statement handle object.
          The returned statement handle can be used to get attributes of the
          statement and invoke the "execute" method. See "Statement Handle
          Methods".
          Drivers for engines without the concept of preparing a statement
          will typically just store the statement in the returned handle and
          process it when "$sth->execute" is called. Such drivers are
          unlikely to give much useful information about the statement, such
          as "$sth->{NUM_OF_FIELDS}", until after "$sth->execute" has been
          called. Portable applications should take this into account.
          In general, DBI drivers do not parse the contents of the statement
          (other than simply counting any "Placeholders"). The statement is
          passed directly to the database engine, sometimes known as pass-
          thru mode. This has advantages and disadvantages. On the plus side,
          you can access all the functionality of the engine being used. On
          the downside, you're limited if you're using a simple engine, and
          you need to take extra care if writing applications intended to be
          portable between engines.
          Portable applications should not assume that a new statement can be
          prepared and/or executed while still fetching results from a previ-
          ous statement.
          Some command-line SQL tools use statement terminators, like a semi-
          colon, to indicate the end of a statement. Such terminators should
          not normally be used with the DBI.
      "prepare_cached"
            $sth = $dbh->prepare_cached($statement)
            $sth = $dbh->prepare_cached($statement, \%attr)
            $sth = $dbh->prepare_cached($statement, \%attr, $if_active)
          Like "prepare" except that the statement handle returned will be
          stored in a hash associated with the $dbh. If another call is made
          to "prepare_cached" with the same $statement and %attr parameter
          values, then the corresponding cached $sth will be returned without
          contacting the database server.
          The $if_active parameter lets you adjust the behaviour if an
          already cached statement handle is still Active.  There are several
          alternatives:
              0: A warning will be generated, and finish() will be called on
              the statement handle before it is returned.  This is the
              default behaviour if $if_active is not passed.
              1: finish() will be called on the statement handle, but the
              warning is suppressed.
              2: Disables any checking.
              3: The existing active statement handle will be removed from
              the cache and a new statement handle prepared and cached in its
              place.  This is the safest option because it doesn't affect the
              state of the old handle, it just removes it from the cache.
              [Added in DBI 1.40]
          Here are some examples of "prepare_cached":
            sub insert_hash {
              my ($table, $field_values) = @_;
              my @fields = sort keys %$field_values; # sort required
              my @values = @{$field_values}{@fields};
              my $sql = sprintf "insert into %s (%s) values (%s)",
                  $table, join(",", @fields), join(",", ("?")x@fields);
              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 @fi

elds;

              $sth = $dbh->prepare_cached("SELECT * FROM $table $qualifier");
              return $dbh->selectall_arrayref($sth, {}, @values);
            }
          Caveat emptor: This caching can be useful in some applications, but
          it can also cause problems and should be used with care. Here is a
          contrived case where caching would cause a significant problem:
            my $sth = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
            $sth->execute(...);
            while (my $data = $sth->fetchrow_hashref) {
              # later, in some other code called within the loop...
              my $sth2 = $dbh->prepare_cached('SELECT * FROM foo WHERE bar=?');
              $sth2->execute(...);
              while (my $data2 = $sth2->fetchrow_arrayref) {
                do_stuff(...);
              }
            }
          In this example, since both handles are preparing the exact same
          statement, $sth2 will not be its own statement handle, but a dupli-
          cate of $sth returned from the cache. The results will certainly
          not be what you expect.  Typically the the inner fetch loop will
          work normally, fetching all the records and terminating when there
          are no more, but now $sth is the same as $sth2 the outer fetch loop
          will also terminate.
          You'll know if you run into this problem because prepare_cached()
          will generate a warning by default (when $if_active is false).
          The cache used by prepare_cached() is keyed by both the statement
          and any attributes so you can also avoid this issue by doing some-
          thing like:
            $sth = $dbh->prepare_cached("...", { dbi_dummy => __FILE__.__LINE__

});

          which will ensure that prepare_cached only returns statements
          cached by that line of code in that source file.
      "commit"
            $rc  = $dbh->commit     or die $dbh->errstr;
          Commit (make permanent) the most recent series of database changes
          if the database supports transactions and AutoCommit is off.
          If "AutoCommit" is on, then calling "commit" will issue a "commit
          ineffective with AutoCommit" warning.
          See also "Transactions" in the "FURTHER INFORMATION" section below.
      "rollback"
            $rc  = $dbh->rollback   or die $dbh->errstr;
          Rollback (undo) the most recent series of uncommitted database
          changes if the database supports transactions and AutoCommit is
          off.
          If "AutoCommit" is on, then calling "rollback" will issue a "roll-
          back ineffective with AutoCommit" warning.
          See also "Transactions" in the "FURTHER INFORMATION" section below.
      "begin_work"
            $rc  = $dbh->begin_work   or die $dbh->errstr;
          Enable transactions (by turning "AutoCommit" off) until the next
          call to "commit" or "rollback". After the next "commit" or "roll-
          back", "AutoCommit" will automatically be turned on again.
          If "AutoCommit" is already off when "begin_work" is called then it
          does nothing except return an error. If the driver does not support
          transactions then when "begin_work" attempts to set "AutoCommit"
          off the driver will trigger a fatal error.
          See also "Transactions" in the "FURTHER INFORMATION" section below.
      "disconnect"
            $rc = $dbh->disconnect  or warn $dbh->errstr;
          Disconnects the database from the database handle. "disconnect" is
          typically only used before exiting the program. The handle is of
          little use after disconnecting.
          The transaction behaviour of the "disconnect" method is, sadly,
          undefined.  Some database systems (such as Oracle and Ingres) will
          automatically commit any outstanding changes, but others (such as
          Informix) will rollback any outstanding changes.  Applications not
          using "AutoCommit" should explicitly call "commit" or "rollback"
          before calling "disconnect".
          The database is automatically disconnected by the "DESTROY" method
          if still connected when there are no longer any references to the
          handle.  The "DESTROY" method for each driver should implicitly
          call "rollback" to undo any uncommitted changes. This is vital
          behaviour to ensure that incomplete transactions don't get commit-
          ted simply because Perl calls "DESTROY" on every object before
          exiting. Also, do not rely on the order of object destruction dur-
          ing "global destruction", as it is undefined.
          Generally, if you want your changes to be commited or rolled back
          when you disconnect, then you should explicitly call "commit" or
          "rollback" before disconnecting.
          If you disconnect from a database while you still have active
          statement handles (e.g., SELECT statement handles that may have
          more data to fetch), you will get a warning. The warning may indi-
          cate that a fetch loop terminated early, perhaps due to an uncaught
          error.  To avoid the warning call the "finish" method on the active
          handles.
      "ping"
            $rc = $dbh->ping;
          Attempts to determine, in a reasonably efficient way, if the
          database server is still running and the connection to it is still
          working.  Individual drivers should implement this function in the
          most suitable manner for their database engine.
          The current default implementation always returns true without
          actually doing anything. Actually, it returns ""0 but true"" which
          is true but zero. That way you can tell if the return value is gen-
          uine or just the default. Drivers should override this method with
          one that does the right thing for their type of database.
          Few applications would have direct use for this method. See the
          specialized Apache::DBI module for one example usage.
      "get_info"
            $value = $dbh->get_info( $info_type );
          Returns information about the implementation, i.e. driver and data
          source capabilities, restrictions etc. It returns "undef" for
          unknown or unimplemented information types. For example:
            $database_version  = $dbh->get_info(  18 ); # SQL_DBMS_VER
            $max_select_tables = $dbh->get_info( 106 ); # SQL_MAXIMUM_TABLES_IN_

SELECT

          See "Standards Reference Information" for more detailed information
          about the information types and their meanings and possible return
          values.
          The DBI::Const::GetInfoType module exports a %GetInfoType hash that
          can be used to map info type names to numbers. For example:
            $database_version = $dbh->get_info( $GetInfoType{SQL_DBMS_VER} );
          The names are a merging of the ANSI and ODBC standards (which dif-
          fer in some cases). See DBI::Const::GetInfoType for more details.
          Because some DBI methods make use of get_info(), drivers are
          strongly encouraged to support at least the following very minimal
          set of information types to ensure the DBI itself works properly:
           Type  Name                        Example A     Example B
           ----  --------------------------  ------------  ----------------
             17  SQL_DBMS_NAME               'ACCESS'      'Oracle'
             18  SQL_DBMS_VER                '03.50.0000'  '08.01.0721 ...'
             29  SQL_IDENTIFIER_QUOTE_CHAR   '`'           '"'
             41  SQL_CATALOG_NAME_SEPARATOR  '.'           '@'
            114  SQL_CATALOG_LOCATION        1             2
      "table_info"
            $sth = $dbh->table_info( $catalog, $schema, $table, $type );
            $sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
          Returns an active statement handle that can be used to fetch infor-
          mation about tables and views that exist in the database.
          The arguments $catalog, $schema and $table may accept search pat-
          terns according to the database/driver, for example: $table =
          '%FOO%'; Remember that the underscore character ('"_"') is a search
          pattern that means match any character, so 'FOO_%' is the same as
          'FOO%' and 'FOO_BAR%' will match names like 'FOO1BAR'.
          The value of $type is a comma-separated list of one or more types
          of tables to be returned in the result set. Each value may option-
          ally be quoted, e.g.:
            $type = "TABLE";
            $type = "'TABLE','VIEW'";
          In addition the following special cases may also be supported by
          some drivers:
          * If the value of $catalog is '%' and $schema and $table name are
          empty strings, the result set contains a list of catalog names. For
          example:
                $sth = $dbh->table_info('%', , );
          * If the value of $schema is '%' and $catalog and $table are empty
          strings, the result set contains a list of schema names.
          * If the value of $type is '%' and $catalog, $schema, and $table
          are all empty strings, the result set contains a list of table
          types.
          If your driver doesn't support one or more of the selection filter
          parameters then you may get back more than you asked for and can do
          the filtering yourself.
          This method can be expensive, and can return a large amount of
          data.  (For example, small Oracle installation returns over 2000
          rows.)  So it's a good idea to use the filters to limit the data as
          much as possible.
          The statement handle returned has at least the following fields in
          the order show below. Other fields, after these, may also be
          present.
          TABLE_CAT: Table catalog identifier. This field is NULL ("undef")
          if not applicable to the data source, which is usually the case.
          This field is empty if not applicable to the table.
          TABLE_SCHEM: The name of the schema containing the TABLE_NAME
          value.  This field is NULL ("undef") if not applicable to data
          source, and empty if not applicable to the table.
          TABLE_NAME: Name of the table (or view, synonym, etc).
          TABLE_TYPE: One of the following: "TABLE", "VIEW", "SYSTEM TABLE",
          "GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM" or a type
          identifier that is specific to the data source.
          REMARKS: A description of the table. May be NULL ("undef").
          Note that "table_info" might not return records for all tables.
          Applications can use any valid table regardless of whether it's
          returned by "table_info".
          See also "tables", "Catalog Methods" and "Standards Reference
          Information".
      "column_info"
            $sth = $dbh->column_info( $catalog, $schema, $table, $column );
          Returns an active statement handle that can be used to fetch infor-
          mation about columns in specified tables.
          The arguments $schema, $table and $column may accept search pat-
          terns according to the database/driver, for example: $table =
          '%FOO%';
          Note: The support for the selection criteria is driver specific. If
          the driver doesn't support one or more of them then you may get
          back more than you asked for and can do the filtering yourself.
          The statement handle returned has at least the following fields in
          the order shown below. Other fields, after these, may also be
          present.
          TABLE_CAT: The catalog identifier.  This field is NULL ("undef") if
          not applicable to the data source, which is often the case.  This
          field is empty if not applicable to the table.
          TABLE_SCHEM: The schema identifier.  This field is NULL ("undef")
          if not applicable to the data source, and empty if not applicable
          to the table.
          TABLE_NAME: The table identifier.  Note: A driver may provide col-
          umn metadata not only for base tables, but also for derived objects
          like SYNONYMS etc.
          COLUMN_NAME: The column identifier.
          DATA_TYPE: The concise data type code.
          TYPE_NAME: A data source dependent data type name.
          COLUMN_SIZE: The column size.  This is the maximum length in char-
          acters for character data types, the number of digits or bits for
          numeric data types or the length in the representation of temporal
          types.  See the relevant specifications for detailed information.
          BUFFER_LENGTH: The length in bytes of transferred data.
          DECIMAL_DIGITS: The total number of significant digits to the right
          of the decimal point.
          NUM_PREC_RADIX: The radix for numeric precision.  The value is 10
          or 2 for numeric data types and NULL ("undef") if not applicable.
          NULLABLE: Indicates if a column can accept NULLs.  The following
          values are defined:
            SQL_NO_NULLS          0
            SQL_NULLABLE          1
            SQL_NULLABLE_UNKNOWN  2
          REMARKS: A description of the column.
          COLUMN_DEF: The default value of the column.
          SQL_DATA_TYPE: The SQL data type.
          SQL_DATETIME_SUB: The subtype code for datetime and interval data
          types.
          CHAR_OCTET_LENGTH: The maximum length in bytes of a character or
          binary data type column.
          ORDINAL_POSITION: The column sequence number (starting with 1).
          IS_NULLABLE: Indicates if the column can accept NULLs.  Possible
          values are: 'NO', 'YES' and .
          SQL/CLI defines the following additional columns:
            CHAR_SET_CAT
            CHAR_SET_SCHEM
            CHAR_SET_NAME
            COLLATION_CAT
            COLLATION_SCHEM
            COLLATION_NAME
            UDT_CAT
            UDT_SCHEM
            UDT_NAME
            DOMAIN_CAT
            DOMAIN_SCHEM
            DOMAIN_NAME
            SCOPE_CAT
            SCOPE_SCHEM
            SCOPE_NAME
            MAX_CARDINALITY
            DTD_IDENTIFIER
            IS_SELF_REF
          Drivers capable of supplying any of those values should do so in
          the corresponding column and supply undef values for the others.
          Drivers wishing to provide extra database/driver specific informa-
          tion should do so in extra columns beyond all those listed above,
          and use lowercase field names with the driver-specific prefix
          (i.e., 'ora_...'). Applications accessing such fields should do so
          by name and not by column number.
          The result set is ordered by TABLE_CAT, TABLE_SCHEM, TABLE_NAME and
          ORDINAL_POSITION.
          Note: There is some overlap with statement attributes (in perl) and
          SQLDescribeCol (in ODBC). However, SQLColumns provides more meta-
          data.
          See also "Catalog Methods" and "Standards Reference Information".
      "primary_key_info"
            $sth = $dbh->primary_key_info( $catalog, $schema, $table );
          Returns an active statement handle that can be used to fetch infor-
          mation about columns that make up the primary key for a table.  The
          arguments don't accept search patterns (unlike table_info()).
          For example:
            $sth = $dbh->primary_key_info( undef, $user, 'foo' );
            $data = $sth->fetchall_arrayref;
          The statement handle will return one row per column, ordered by TA-
          BLE_CAT, TABLE_SCHEM, TABLE_NAME, and KEY_SEQ.
          Note: The support for the selection criteria, such as $catalog, is
          driver specific.  If the driver doesn't support catalogs and/or
          schemas, it may ignore these criteria.
          The statement handle returned has at least the following fields in
          the order shown below. Other fields, after these, may also be
          present.
          TABLE_CAT: The catalog identifier.  This field is NULL ("undef") if
          not applicable to the data source, which is often the case.  This
          field is empty if not applicable to the table.
          TABLE_SCHEM: The schema identifier.  This field is NULL ("undef")
          if not applicable to the data source, and empty if not applicable
          to the table.
          TABLE_NAME: The table identifier.
          COLUMN_NAME: The column identifier.
          KEY_SEQ: The column sequence number (starting with 1).  Note: This
          field is named ORDINAL_POSITION in SQL/CLI.
          PK_NAME: The primary key constraint identifier.  This field is NULL
          ("undef") if not applicable to the data source.
          See also "Catalog Methods" and "Standards Reference Information".
      "primary_key"
            @key_column_names = $dbh->primary_key( $catalog, $schema, $table );
          Simple interface to the primary_key_info() method. Returns a list
          of the column names that comprise the primary key of the specified
          table.  The list is in primary key column sequence order.
      "foreign_key_info"
            $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
                                         , $fk_catalog, $fk_schema, $fk_table );
            $sth = $dbh->foreign_key_info( $pk_catalog, $pk_schema, $pk_table
                                         , $fk_catalog, $fk_schema, $fk_table
                                         , \%attr );
          Returns an active statement handle that can be used to fetch infor-
          mation about foreign keys in and/or referencing the specified ta-
          ble(s).  The arguments don't accept search patterns (unlike ta-
          ble_info()).
          $pk_catalog, $pk_schema, $pk_table identify the primary (unique)
          key table (PKT).
          $fk_catalog, $fk_schema, $fk_table identify the foreign key table
          (FKT).
          If both PKT and FKT are given, the function returns the foreign
          key, if any, in table FKT that refers to the primary (unique) key
          of table PKT.  (Note: In SQL/CLI, the result is implementa-
          tion-defined.)
          If only PKT is given, then the result set contains the primary key
          of that table and all foreign keys that refer to it.
          If only FKT is given, then the result set contains all foreign keys
          in that table and the primary keys to which they refer.  (Note: In
          SQL/CLI, the result includes unique keys too.)
          For example:
            $sth = $dbh->foreign_key_info( undef, $user, 'master');
            $sth = $dbh->foreign_key_info( undef, undef,   undef , undef, $user,
'detail');
            $sth = $dbh->foreign_key_info( undef, $user, 'master', undef, $user,
'detail');
          Note: The support for the selection criteria, such as $catalog, is
          driver specific.  If the driver doesn't support catalogs and/or
          schemas, it may ignore these criteria.
          The statement handle returned has the following fields in the order
          shown below.  Because ODBC never includes unique keys, they define
          different columns in the result set than SQL/CLI. SQL/CLI column
          names are shown in parentheses.
          PKTABLE_CAT    ( UK_TABLE_CAT      ): The primary (unique) key ta-
          ble catalog identifier.  This field is NULL ("undef") if not appli-
          cable to the data source, which is often the case.  This field is
          empty if not applicable to the table.
          PKTABLE_SCHEM  ( UK_TABLE_SCHEM    ): The primary (unique) key ta-
          ble schema identifier.  This field is NULL ("undef") if not appli-
          cable to the data source, and empty if not applicable to the table.
          PKTABLE_NAME   ( UK_TABLE_NAME     ): The primary (unique) key ta-
          ble identifier.
          PKCOLUMN_NAME  (UK_COLUMN_NAME    ): The primary (unique) key col-
          umn identifier.
          FKTABLE_CAT    ( FK_TABLE_CAT      ): The foreign key table catalog
          identifier.  This field is NULL ("undef") if not applicable to the
          data source, which is often the case.  This field is empty if not
          applicable to the table.
          FKTABLE_SCHEM  ( FK_TABLE_SCHEM    ): The foreign key table schema
          identifier.  This field is NULL ("undef") if not applicable to the
          data source, and empty if not applicable to the table.
          FKTABLE_NAME   ( FK_TABLE_NAME     ): The foreign key table identi-
          fier.
          FKCOLUMN_NAME  ( FK_COLUMN_NAME    ): The foreign key column iden-
          tifier.
          KEY_SEQ        ( ORDINAL_POSITION  ): The column sequence number
          (starting with 1).
          UPDATE_RULE    ( UPDATE_RULE       ): The referential action for
          the UPDATE rule.  The following codes are defined:
            CASCADE              0
            RESTRICT             1
            SET NULL             2
            NO ACTION            3
            SET DEFAULT          4
          DELETE_RULE    ( DELETE_RULE       ): The referential action for
          the DELETE rule.  The codes are the same as for UPDATE_RULE.
          FK_NAME        ( FK_NAME           ): The foreign key name.
          PK_NAME        ( UK_NAME           ): The primary (unique) key
          name.
          DEFERRABILITY  ( DEFERABILITY      ): The deferrability of the for-
          eign key constraint.  The following codes are defined:
            INITIALLY DEFERRED   5
            INITIALLY IMMEDIATE  6
            NOT DEFERRABLE       7
                         ( UNIQUE_OR_PRIMARY ): This column is necessary if a
          driver includes all candidate (i.e. primary and alternate) keys in
          the result set (as specified by SQL/CLI).  The value of this column
          is UNIQUE if the foreign key references an alternate key and PRI-
          MARY if the foreign key references a primary key, or it may be
          undefined if the driver doesn't have access to the information.
          See also "Catalog Methods" and "Standards Reference Information".
      "tables"
            @names = $dbh->tables( $catalog, $schema, $table, $type );
            @names = $dbh->tables;        # deprecated
          Simple interface to table_info(). Returns a list of matching table
          names, possibly including a catalog/schema prefix.
          See "table_info" for a description of the parameters.
          If "$dbh->get_info(29)" returns true (29 is SQL_IDENTI-
          FIER_QUOTE_CHAR) then the table names are constructed and quoted by
          "quote_identifier" to ensure they are usable even if they contain
          whitespace or reserved words etc. This means that the table names
          returned will include quote characters.
      "type_info_all"
            $type_info_all = $dbh->type_info_all;
          Returns a reference to an array which holds information about each
          data type variant supported by the database and driver. The array
          and its contents should be treated as read-only.
          The first item is a reference to an 'index' hash of "Name =">
          "Index" pairs.  The items following that are references to arrays,
          one per supported data type variant. The leading index hash defines
          the names and order of the fields within the arrays that follow it.
          For example:
            $type_info_all = [
              {   TYPE_NAME         => 0,
                  DATA_TYPE         => 1,
                  COLUMN_SIZE       => 2,     # was PRECISION originally
                  LITERAL_PREFIX    => 3,
                  LITERAL_SUFFIX    => 4,
                  CREATE_PARAMS     => 5,
                  NULLABLE          => 6,
                  CASE_SENSITIVE    => 7,
                  SEARCHABLE        => 8,
                  UNSIGNED_ATTRIBUTE=> 9,
                  FIXED_PREC_SCALE  => 10,    # was MONEY originally
                  AUTO_UNIQUE_VALUE => 11,    # was AUTO_INCREMENT originally
                  LOCAL_TYPE_NAME   => 12,
                  MINIMUM_SCALE     => 13,
                  MAXIMUM_SCALE     => 14,
                  SQL_DATA_TYPE     => 15,
                  SQL_DATETIME_SUB  => 16,
                  NUM_PREC_RADIX    => 17,
                  INTERVAL_PRECISION=> 18,
              },
              [ 'VARCHAR', SQL_VARCHAR,
                  undef, "'","'", undef,0, 1,1,0,0,0,undef,1,255, undef
              ],
              [ 'INTEGER', SQL_INTEGER,
                  undef,  "", "", undef,0, 0,1,0,0,0,undef,0,  0, 10
              ],
            ];
          More than one row may have the same value in the "DATA_TYPE" field
          if there are different ways to spell the type name and/or there are
          variants of the type with different attributes (e.g., with and
          without "AUTO_UNIQUE_VALUE" set, with and without
          "UNSIGNED_ATTRIBUTE", etc).
          The rows are ordered by "DATA_TYPE" first and then by how closely
          each type maps to the corresponding ODBC SQL data type, closest
          first.
          The meaning of the fields is described in the documentation for the
          "type_info" method.
          An 'index' hash is provided so you don't need to rely on index val-
          ues defined above.  However, using DBD::ODBC with some old ODBC
          drivers may return older names, shown as comments in the example
          above.  Another issue with the index hash is that the lettercase of
          the keys is not defined. It is usually uppercase, as show here, but
          drivers may return names with any lettercase.
          Drivers are also free to return extra driver-specific columns of
          information - though it's recommended that they start at column
          index 50 to leave room for expansion of the DBI/ODBC specification.
          The type_info_all() method is not normally used directly.  The
          "type_info" method provides a more usable and useful interface to
          the data.
      "type_info"
            @type_info = $dbh->type_info($data_type);
          Returns a list of hash references holding information about one or
          more variants of $data_type. The list is ordered by "DATA_TYPE"
          first and then by how closely each type maps to the corresponding
          ODBC SQL data type, closest first.  If called in a scalar context
          then only the first (best) element is returned.
          If $data_type is undefined or "SQL_ALL_TYPES", then the list will
          contain hashes for all data type variants supported by the database
          and driver.
          If $data_type is an array reference then "type_info" returns the
          information for the first type in the array that has any matches.
          The keys of the hash follow the same letter case conventions as the
          rest of the DBI (see "Naming Conventions and Name Space"). The fol-
          lowing uppercase items should always exist, though may be undef:
          TYPE_NAME (string)
              Data type name for use in CREATE TABLE statements etc.
          DATA_TYPE (integer)
              SQL data type number.
          COLUMN_SIZE (integer)
              For numeric types, this is either the total number of digits
              (if the NUM_PREC_RADIX value is 10) or the total number of bits
              allowed in the column (if NUM_PREC_RADIX is 2).
              For string types, this is the maximum size of the string in
              characters.
              For date and interval types, this is the maximum number of
              characters needed to display the value.
          LITERAL_PREFIX (string)
              Characters used to prefix a literal. A typical prefix is ""'""
              for characters, or possibly ""0x"" for binary values passed as
              hexadecimal.  NULL ("undef") is returned for data types for
              which this is not applicable.
          LITERAL_SUFFIX (string)
              Characters used to suffix a literal. Typically ""'"" for char-
              acters.  NULL ("undef") is returned for data types where this
              is not applicable.
          CREATE_PARAMS (string)
              Parameter names for data type definition. For example, "CRE-
              ATE_PARAMS" for a "DECIMAL" would be ""precision,scale"" if the
              DECIMAL type should be declared as "DECIMAL("precision,scale")"
              where precision and scale are integer values.  For a "VARCHAR"
              it would be ""max length"".  NULL ("undef") is returned for
              data types for which this is not applicable.
          NULLABLE (integer)
              Indicates whether the data type accepts a NULL value: 0 or an
              empty string = no, 1 = yes, 2 = unknown.
          CASE_SENSITIVE (boolean)
              Indicates whether the data type is case sensitive in collations
              and comparisons.
          SEARCHABLE (integer)
              Indicates how the data type can be used in a WHERE clause, as
              follows:
                0 - Cannot be used in a WHERE clause
                1 - Only with a LIKE predicate
                2 - All comparison operators except LIKE
                3 - Can be used in a WHERE clause with any comparison operator
          UNSIGNED_ATTRIBUTE (boolean)
              Indicates whether the data type is unsigned.  NULL ("undef") is
              returned for data types for which this is not applicable.
          FIXED_PREC_SCALE (boolean)
              Indicates whether the data type always has the same precision
              and scale (such as a money type).  NULL ("undef") is returned
              for data types for which this is not applicable.
          AUTO_UNIQUE_VALUE (boolean)
              Indicates whether a column of this data type is automatically
              set to a unique value whenever a new row is inserted.  NULL
              ("undef") is returned for data types for which this is not
              applicable.
          LOCAL_TYPE_NAME (string)
              Localized version of the "TYPE_NAME" for use in dialog with
              users.  NULL ("undef") is returned if a localized name is not
              available (in which case "TYPE_NAME" should be used).
          MINIMUM_SCALE (integer)
              The minimum scale of the data type. If a data type has a fixed
              scale, then "MAXIMUM_SCALE" holds the same value.  NULL
              ("undef") is returned for data types for which this is not
              applicable.
          MAXIMUM_SCALE (integer)
              The maximum scale of the data type. If a data type has a fixed
              scale, then "MINIMUM_SCALE" holds the same value.  NULL
              ("undef") is returned for data types for which this is not
              applicable.
          SQL_DATA_TYPE (integer)
              This column is the same as the "DATA_TYPE" column, except for
              interval and datetime data types.  For interval and datetime
              data types, the "SQL_DATA_TYPE" field will return "SQL_INTER-
              VAL" or "SQL_DATETIME", and the "SQL_DATETIME_SUB" field below
              will return the subcode for the specific interval or datetime
              data type. If this field is NULL, then the driver does not sup-
              port or report on interval or datetime subtypes.
          SQL_DATETIME_SUB (integer)
              For interval or datetime data types, where the "SQL_DATA_TYPE"
              field above is "SQL_INTERVAL" or "SQL_DATETIME", this field
              will hold the subcode for the specific interval or datetime
              data type.  Otherwise it will be NULL ("undef").
              Although not mentioned explicitly in the standards, it seems
              there is a simple relationship between these values:
                DATA_TYPE == (10 * SQL_DATA_TYPE) + SQL_DATETIME_SUB
          NUM_PREC_RADIX (integer)
              The radix value of the data type. For approximate numeric
              types, "NUM_PREC_RADIX" contains the value 2 and "COLUMN_SIZE"
              holds the number of bits. For exact numeric types,
              "NUM_PREC_RADIX" contains the value 10 and "COLUMN_SIZE" holds
              the number of decimal digits. NULL ("undef") is returned either
              for data types for which this is not applicable or if the
              driver cannot report this information.
          INTERVAL_PRECISION (integer)
              The interval leading precision for interval types. NULL is
              returned either for data types for which this is not applicable
              or if the driver cannot report this information.
          For example, to find the type name for the fields in a select
          statement you can do:
            @names = map { scalar $dbh->type_info($_)->{TYPE_NAME} } @{ $sth->{T

YPE} }

          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 'Dont' (including the
          outer quotation marks).
          An undefined $value value will be returned as the string "NULL"
          (without single quotation marks) to match how NULLs are represented
          in SQL.
          If $data_type is supplied, it is used to try to determine the
          required quoting behaviour by using the information returned by
          "type_info".  As a special case, the standard numeric types are
          optimized to return $value without calling "type_info".
          Quote will probably not be able to deal with all possible input
          (such as binary data or data containing newlines), and is not
          related in any way with escaping or quoting shell meta-characters.
          It is valid for the quote() method to return an SQL expression that
          evaluates to the desired string. For example:
            $quoted = $dbh->quote("one\ntwo\0three")
          may return something like:
            CONCAT('one', CHAR(12), 'two', CHAR(0), 'three')
          The quote() method should not be used with "Placeholders and Bind
          Values".
      "quote_identifier"
            $sql = $dbh->quote_identifier( $name );
            $sql = $dbh->quote_identifier( $catalog, $schema, $table, \%attr );
          Quote an identifier (table name etc.) for use in an SQL statement,
          by escaping any special characters (such as double quotation marks)
          it contains and adding the required type of outer quotation marks.
          Undefined names are ignored and the remainder are quoted and then
          joined together, typically with a dot (".") character. For example:
            $id = $dbh->quote_identifier( undef, 'Her schema', 'My table' );
          would, for most database types, return "Her schema"."My table"
          (including all the double quotation marks).
          If three names are supplied then the first is assumed to be a cata-
          log name and special rules may be applied based on what "get_info"
          returns for SQL_CATALOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCA-
          TION (114).  For example, for Oracle:
            $id = $dbh->quote_identifier( 'link', 'schema', 'table' );
          would return "schema"."table"@"link".
      "take_imp_data"
            $imp_data = $dbh->take_imp_data;
          Leaves the $dbh in an almost dead, zombie-like, state and returns a
          binary string of raw implementation data from the driver which
          describes the current database connection. Effectively it detaches
          the underlying database API connection data from the DBI handle.
          After calling take_imp_data(), all other methods except "DESTROY"
          will generate a warning and return undef.
          Why would you want to do this? You don't, forget I even mentioned
          it.  Unless, that is, you're implementing something advanced like a
          multi-threaded connection pool.
          The returned $imp_data can be passed as a "dbi_imp_data" attribute
          to a later connect() call, even in a separate thread in the same
          process, where the driver can use it to 'adopt' the existing con-
          nection that the implementation data was taken from.
          Some things to keep in mind...
          * the $imp_data holds the only reference to the underlying database
          API connection data. That connection is still 'live' and won't be
          cleaned up properly unless the $imp_data is used to create a new
          $dbh which can then disconnect() normally.
          * using the same $imp_data to create more than one other new $dbh
          at a time may well lead to unpleasant problems. Don't do that.
          The "take_imp_data" method was added in DBI 1.36.
      Database Handle Attributes
      This section describes attributes specific to database handles.
      Changes to these database handle attributes do not affect any other
      existing or future database handles.
      Attempting to set or get the value of an unknown attribute generates a
      warning, except for private driver-specific attributes (which all have
      names starting with a lowercase letter).
      Example:
        $h->{AutoCommit} = ...;       # set/write
        ... = $h->{AutoCommit};       # get/read
      "AutoCommit"  (boolean)
          If true, then database changes cannot be rolled-back (undone).  If
          false, then database changes automatically occur within a "transac-
          tion", which must either be committed or rolled back using the
          "commit" or "rollback" methods.
          Drivers should always default to "AutoCommit" mode (an unfortunate
          choice largely forced on the DBI by ODBC and JDBC conventions.)
          Attempting to set "AutoCommit" to an unsupported value is a fatal
          error.  This is an important feature of the DBI. Applications that
          need full transaction behaviour can set "$dbh->{AutoCommit} = 0"
          (or set "AutoCommit" to 0 via "connect") without having to check
          that the value was assigned successfully.
          For the purposes of this description, we can divide databases into
          three categories:
            Databases which don't support transactions at all.
            Databases in which a transaction is always active.
            Databases in which a transaction must be explicitly started (C<'BEGI

N WORK'>).

          * Databases which don't support transactions at all
          For these databases, attempting to turn "AutoCommit" off is a fatal
          error.  "commit" and "rollback" both issue warnings about being
          ineffective while "AutoCommit" is in effect.
          * Databases in which a transaction is always active
          These are typically mainstream commercial relational databases with
          "ANSI standard" transaction behaviour.  If "AutoCommit" is off,
          then changes to the database won't have any lasting effect unless
          "commit" is called (but see also "disconnect"). If "rollback" is
          called then any changes since the last commit are undone.
          If "AutoCommit" is on, then the effect is the same as if the DBI
          called "commit" automatically after every successful database oper-
          ation. So calling "commit" or "rollback" explicitly while "AutoCom-
          mit" is on would be ineffective because the changes would have
          already been commited.
          Changing "AutoCommit" from off to on will trigger a "commit".
          For databases which don't support a specific auto-commit mode, the
          driver has to commit each statement automatically using an explicit
          "COMMIT" after it completes successfully (and roll it back using an
          explicit "ROLLBACK" if it fails).  The error information reported
          to the application will correspond to the statement which was exe-
          cuted, unless it succeeded and the commit or rollback failed.
          * Databases in which a transaction must be explicitly started
          For these databases, the intention is to have them act like
          databases in which a transaction is always active (as described
          above).
          To do this, the driver will automatically begin an explicit trans-
          action when "AutoCommit" is turned off, or after a "commit" or
          "rollback" (or when the application issues the next database opera-
          tion after one of those events).
          In this way, the application does not have to treat these databases
          as a special case.
          See "commit", "disconnect" and "Transactions" for other important
          notes about transactions.
      "Driver"  (handle)
          Holds the handle of the parent driver. The only recommended use for
          this is to find the name of the driver using:
            $dbh->{Driver}->{Name}
      "Name"  (string)
          Holds the "name" of the database. Usually (and recommended to be)
          the same as the ""dbi:DriverName:..."" string used to connect to
          the database, but with the leading ""dbi:DriverName:"" removed.
      "Statement"  (string, read-only)
          Returns the statement string passed to the most recent "prepare"
          method called in this database handle, even if that method failed.
          This is especially useful where "RaiseError" is enabled and the
          exception handler checks $@ and sees that a 'prepare' method call
          failed.
      "RowCacheSize"  (integer)
          A hint to the driver indicating the size of the local row cache
          that the application would like the driver to use for future
          "SELECT" statements.  If a row cache is not implemented, then set-
          ting "RowCacheSize" is ignored and getting the value returns
          "undef".
          Some "RowCacheSize" values have special meaning, as follows:
            0 - Automatically determine a reasonable cache size for each C<SELEC

T>

            1 - Disable the local row cache
           >1 - Cache this many rows
           <0 - Cache as many rows that will fit into this much memory for each

C<SELECT>.

          Note that large cache sizes may require a very large amount of mem-
          ory (cached rows * maximum size of row). Also, a large cache will
          cause a longer delay not only for the first fetch, but also when-
          ever the cache needs refilling.
          See also the "RowsInCache" statement handle attribute.
      "Username"  (string)
          Returns the username used to connect to the database.

DBI STATEMENT HANDLE OBJECTS

      This section lists the methods and attributes associated with DBI
      statement handles.
      Statement Handle Methods
      The DBI defines the following methods for use on DBI statement handles:
      "bind_param"
            $sth->bind_param($p_num, $bind_value)
            $sth->bind_param($p_num, $bind_value, \%attr)
            $sth->bind_param($p_num, $bind_value, $bind_type)
          The "bind_param" method takes a copy of $bind_value and associates
          it (binds it) with a placeholder, identified by $p_num, embedded in
          the prepared statement. Placeholders are indicated with question
          mark character ("?"). For example:
            $dbh->{RaiseError} = 1;        # save having to check each method ca

ll

            $sth = $dbh->prepare("SELECT name, age FROM people WHERE name LIKE ?

");

            $sth->bind_param(1, "John%");  # placeholders are numbered from 1
            $sth->execute;
            DBI::dump_results($sth);
          See "Placeholders and Bind Values" for more information.
          Data Types for Placeholders
          The "\%attr" parameter can be used to hint at the data type the
          placeholder should have. Typically, the driver is only interested
          in knowing if the placeholder should be bound as a number or a
          string.
            $sth->bind_param(1, $value, { TYPE => SQL_INTEGER });
          As a short-cut for the common case, the data type can be passed
          directly, in place of the "\%attr" hash reference. This example is
          equivalent to the one above:
            $sth->bind_param(1, $value, SQL_INTEGER);
          The "TYPE" value indicates the standard (non-driver-specific) type
          for this parameter. To specify the driver-specific type, the driver
          may support a driver-specific attribute, such as "{ ora_type => 97
          }".
          The SQL_INTEGER and other related constants can be imported using
            use DBI qw(:sql_types);
          See "DBI Constants" for more information.
          The data type for a placeholder cannot be changed after the first
          "bind_param" call. In fact the whole \%attr parameter is 'sticky'
          in the sense that a driver only needs to consider the \%attr param-
          eter for the first call, for a given $sth and parameter. After that
          the driver may ignore the \%attr parameter for that placeholder.
          Perl only has string and number scalar data types. All database
          types that aren't numbers are bound as strings and must be in a
          format the database will understand except where the bind_param()
          TYPE attribute specifies a type that implies a particular format.
          For example, given:
            $sth->bind_param(1, $value, SQL_DATETIME);
          the driver should expect $value to be in the ODBC standard
          SQL_DATETIME format, which is 'YYYY-MM-DD HH:MM:SS'. Similarly for
          SQL_DATE, SQL_TIME etc.
          As an alternative to specifying the data type in the "bind_param"
          call, you can let the driver pass the value as the default type
          ("VARCHAR").  You can then use an SQL function to convert the type
          within the statement.  For example:
            INSERT INTO price(code, price) VALUES (?, CONVERT(MONEY,?))
          The "CONVERT" function used here is just an example. The actual
          function and syntax will vary between different databases and is
          non-portable.
          See also "Placeholders and Bind Values" for more information.
      "bind_param_inout"
            $rc = $sth->bind_param_inout($p_num, \$bind_value, $max_len)  or die
$sth->errstr;
            $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, \%attr)
    or ...
            $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, $bind_t

ype) or ...

          This method acts like "bind_param", but also enables values to be
          updated by the statement. The statement is typically a call to a
          stored procedure. The $bind_value must be passed as a reference to
          the actual value to be used.
          Note that unlike "bind_param", the $bind_value variable is not
          copied when "bind_param_inout" is called. Instead, the value in the
          variable is read at the time "execute" is called.
          The additional $max_len parameter specifies the minimum amount of
          memory to allocate to $bind_value for the new value. If the value
          returned from the database is too big to fit, then the execution
          should fail. If unsure what value to use, pick a generous length,
          i.e., a length larger than the longest value that would ever be
          returned.  The only cost of using a larger value than needed is
          wasted memory.
          Undefined values or "undef" are used to indicate null values.  See
          also "Placeholders and Bind Values" for more information.
      "bind_param_array"
            $rc = $sth->bind_param_array($p_num, $array_ref_or_value)
            $rc = $sth->bind_param_array($p_num, $array_ref_or_value, \%attr)
            $rc = $sth->bind_param_array($p_num, $array_ref_or_value, $bind_type

)

          The "bind_param_array" method is used to bind an array of values to
          a placeholder embedded in the prepared statement which is to be
          executed with "execute_array". For example:
            $dbh->{RaiseError} = 1;        # save having to check each method ca

ll

            $sth = $dbh->prepare("INSERT INTO staff (first_name, last_name, dept

) VALUES(?, ?, ?)");

            $sth->bind_param_array(1, [ 'John', 'Mary', 'Tim' ]);
            $sth->bind_param_array(2, [ 'Booth', 'Todd', 'Robinson' ]);
            $sth->bind_param_array(3, "SALES"); # scalar will be reused for each
row
            $sth->execute_array( { ArrayTupleStatus => \my @tuple_status } );
          The %attr ($bind_type) argument is the same as defined for
          "bind_param".  Refer to "bind_param" for general details on using
          placeholders.
          (Note that bind_param_array() can not be used to expand a place-
          holder into a list of values for a statement like "SELECT foo WHERE
          bar IN (?)".  A placeholder can only ever represent one value per
          execution.)
          Scalar values, including "undef", may also be bound by
          "bind_param_array". In which case the same value will be used for
          each "execute" call. Driver-specific implementations may behave
          differently, e.g., when binding to a stored procedure call, some
          databases may permit mixing scalars and arrays as arguments.
          The default implementation provided by DBI (for drivers that have
          not implemented array binding) is to iteratively call "execute" for
          each parameter tuple provided in the bound arrays.  Drivers may
          provide more optimized implementations using whatever bulk opera-
          tion support the database API provides. The default driver
          behaviour should match the default DBI behaviour, but always con-
          sult your driver documentation as there may be driver specific
          issues to consider.
          Note that the default implementation currently only supports non-
          data returning statements (INSERT, UPDATE, but not SELECT). Also,
          "bind_param_array" and "bind_param" cannot be mixed in the same
          statement execution, and "bind_param_array" must be used with "exe-
          cute_array"; using "bind_param_array" will have no effect for "exe-
          cute".
          The "bind_param_array" method was added in DBI 1.22.
      "execute"
            $rv = $sth->execute                or die $sth->errstr;
            $rv = $sth->execute(@bind_values)  or die $sth->errstr;
          Perform whatever processing is necessary to execute the prepared
          statement.  An "undef" is returned if an error occurs.  A success-
          ful "execute" always returns true regardless of the number of rows
          affected, even if it's zero (see below). It is always important to
          check the return status of "execute" (and most other DBI methods)
          for errors if you're not using "RaiseError".
          For a non-"SELECT" statement, "execute" returns the number of rows
          affected, if known. If no rows were affected, then "execute"
          returns "0E0", which Perl will treat as 0 but will regard as true.
          Note that it is not an error for no rows to be affected by a state-
          ment. If the number of rows affected is not known, then "execute"
          returns -1.
          For "SELECT" statements, execute simply "starts" the query within
          the database engine. Use one of the fetch methods to retrieve the
          data after calling "execute".  The "execute" method does not return
          the number of rows that will be returned by the query (because most
          databases can't tell in advance), it simply returns a true value.
          If any arguments are given, then "execute" will effectively call
          "bind_param" for each value before executing the statement.  Values
          bound in this way are usually treated as "SQL_VARCHAR" types unless
          the driver can determine the correct type (which is rare), or
          unless "bind_param" (or "bind_param_inout") has already been used

Edit Notes

  • 2006-06-09 Transcribed up to Manual page DBI(3pm) line 3093