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);
         $ary_ref = $dbh->selectall_hashref($statement);

         $ary_ref = $dbh->selectcol_arrayref($statement);

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

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

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

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

         $rc = $sth->bind_col($col_num, \$col_variable);
         $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);

         @row_ary  = $sth->fetchrow_array;
         $ary_ref  = $sth->fetchrow_arrayref;
         $hash_ref = $sth->fetchrow_hashref;

         $ary_ref  = $sth->fetchall_arrayref;

         $rv  = $sth->rows;

         $rc  = $dbh->commit;
         $rc  = $dbh->rollback;

         $sql = $dbh->quote($string);

         $rc  = $h->err;
         $str = $h->errstr;
         $rv  = $h->state;

         $rc  = $dbh->disconnect;


       GETTING HELP

       If you have questions about DBI, you can get help from the
       dbi-users@perl.org mailing list.  You can subscribe to the
       list by emailing:

         dbi-users-help@perl.org

       Also worth a visit is the DBI home page at:

         http://dbi.perl.org/

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

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

       NOTE

       This is the DBI specification that corresponds to the DBI
       version 1.17 (`$Date: 2001/06/04 17:20:21 $').

       The DBI specification is evolving at a steady pace, so
       it's important to check that you have the latest copy. The
       RECENT CHANGES section below has a summary of user-visible
       changes. The Changes file supplied with the DBI holds more
       detailed change information.

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

       Extensions to the DBI and other DBI related modules use
       the `DBIx::*' namespace. See the Naming Conventions and
       Name Space entry elsewhere in this document and:

         http://www.perl.com/CPAN/modules/by-module/DBIx/


       Here is a brief summary of significant user-visible
       changes in recent versions.  (If a recent version isn't
       mentioned, it simply means that there were no significant
       user-visible changes in that version.)

       DBI 1.15
           Added selectall_hashref, selectrow_hashref, selec­
           trow_arrayref methods.


DESCRIPTION

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

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

       Architecture of a DBI Application

                    |<- 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.


       The following conventions are used in this document:

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

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

       Outline Usage

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

         use DBI;
         use strict;

       (The `use strict;' isn't required but is strongly recom­
       mended.)

       Then you need to the connect entry elsewhere in this docu­
       ment to your data source and get a handle for that connec­
       tion:

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

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

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

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

       The typical method call sequence for a `SELECT' statement
       is:

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

       for example:

         $sth = $dbh->prepare("SELECT foo, bar FROM table WHERE baz=?");

         $sth->execute( $baz );

         while ( @row = $sth->fetchrow_array ) {
           print "@row\n";
         }

       The typical method call sequence for a non-`SELECT' state­
       ment is:

         prepare,
           execute,
           execute,
           execute.

       for example:

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

         while(<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 the AutoCom­
       mit entry elsewhere in this document is off):

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

       Finally, when you have finished working with the data
       source, you should the disconnect entry elsewhere in this
       document from it:

         $dbh->disconnect;


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

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

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

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

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

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

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

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

       Individual driver implementors are free to provide any
       private functions and/or handle attributes that they feel
       are useful.  Private driver functions can be invoked using
       the DBI `func()' method.  Private driver attributes are
       accessed just like standard attributes.

       Many methods have an optional `\%attr' parameter which can
       be used to pass information to the driver implementing the
       method. Except where specifically documented, the `\%attr'

       In general, you can ignore `\%attr' parameters or pass it
       as `undef'.

       Naming Conventions and Name Space

       The DBI package and all packages below it (`DBI::*') are
       reserved for use by the DBI. Extensions and related mod­
       ules use the `DBIx::' namespace (see
       `http://www.perl.com/CPAN/modules/by-module/DBIx/').
       Package names beginning with `DBD::' are reserved for use
       by DBI database drivers.  All environment variables used
       by the DBI or by individual DBDs begin with "`DBI_'" or
       "`DBD_'".

       The letter case used for attribute names is significant
       and plays an important part in the portability of DBI
       scripts.  The case of the attribute name is used to sig­
       nify who defined the meaning of that name and its values.

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

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

       Driver Specific Prefix Registry:

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

       SQL - A Query Language

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

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

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

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

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

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


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

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

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

         SELECT description FROM products WHERE product_code = ?

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

       When using placeholders with the SQL `LIKE' qualifier, you
       must remember that the placeholder substitutes for the
       whole string.  So you should use "`... LIKE ? ...'" and
       include any wildcard characters in the value that you bind
       to the placeholder.

       Null Values

       Undefined values, or `undef', can be used to indicate null
       values.  However, care must be taken in the particular
       case of trying to use null values to qualify a `SELECT'
       statement. Consider:

         SELECT description FROM products WHERE product_code = ?

       Binding an `undef' (NULL) to the placeholder will not
       select rows which have a NULL `product_code'! Refer to the
       SQL manual for your database engine or any SQL book for
       the reasons for this.  To explicitly select NULLs you have
       to say "`WHERE product_code IS NULL'" and to make that
       general you have to say:

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

       and bind the same value to both placeholders.

       Performance

       Without using placeholders, the insert statement shown
       previously would have to contain the literal values to be
       inserted and would have to be re-prepared and re-executed
       for each row. With placeholders, the insert statement only
       needs to be prepared once. The bind values for each row
       can be given to the `execute' method each time it's
       called. By avoiding the need to re-prepare the statement

       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 the executeand bind_param entries elsewhere in this
       document for more details.

       The `q{...}' style quoting used in this example avoids
       clashing with quotes that may be used in the SQL state­
       ment. Use the double-quote like `qq{...}' operator if you
       want to interpolate variables into the string.  See the
       Quote and Quote-like Operators entry in the perlop manpage
       for more details.

       See also the the bind_column entry elsewhere in this docu­
       ment 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

       The following SQL standard type constants can be imported
       individually or, by importing the special `:sql_types'
       tag, all together:

         SQL_CHAR SQL_NUMERIC SQL_DECIMAL SQL_INTEGER SQL_SMALLINT
         SQL_FLOAT SQL_REAL SQL_DOUBLE SQL_VARCHAR
         SQL_DATE SQL_TIME SQL_TIMESTAMP
         SQL_LONGVARCHAR SQL_BINARY SQL_VARBINARY SQL_LONGVARBINARY
         SQL_BIGINT SQL_TINYINT
         SQL_WCHAR SQL_WVARCHAR SQL_WLONGVARCHAR
         SQL_BIT
         SQL_ALL_TYPES

       See the the type_info, type_info_all, and bind_param
       entries elsewhere in this document methods for possible
       uses.


       The following methods are provided by the DBI class:

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

           Establishes a database connection, or session, to the
           requested `$data_source'.  Returns a database handle
           object if the connection succeeds. Use `$dbh-'>`dis­
           connect' to terminate the connection.

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

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

           The `$data_source' value should begin with
           "`dbi:'driver_name`:'". The driver_name specifies the
           driver that will be used to make the connection. (Let­
           ter case is significant.)

           As a convenience, if the `$data_source' parameter is
           undefined or empty, the DBI will substitute the value
           of the environment variable `DBI_DSN'.  If just the
           driver_name part is empty (i.e., the `$data_source'
           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.)

           (and the driver in `$data_source' is not "`Proxy'")
           then the connect request will automatically be changed
           to:

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

           and passed to the DBD::Proxy module. `DBI_AUTOPROXY'
           is typically set as "`hostname=...;port=...'". See the
           DBD::Proxy documentation for more details.

           If `$username' or `$password' are undefined (rather
           than just empty), then the DBI will substitute the
           values of the `DBI_USER' and `DBI_PASS' environment
           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.

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

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

           The `AutoCommit' and `PrintError' attributes for each
           connection default to "on". (See the AutoCommitand
           PrintError entries elsewhere in this document for more
           information.)  However, it is strongly recommended
           that you explicitly define `AutoCommit' rather than
           rely on the default. Future versions of the DBI may
           issue a warning if `AutoCommit' is not explicitly
           defined.

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

                   PrintError => 0,
                   AutoCommit => 0
             });

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

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

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

           The `dbi_connect_method' attribute can be used to
           specify which driver method should be called to estab­
           lish the connection. The only useful values are 'con­
           nect', 'connect_cached', or some specialized case like
           'Apache::DBI::connect' (which is automatically the
           default when running within Apache).

           Where possible, each session (`$dbh') is independent
           from the transactions in other sessions. This is use­
           ful when you need to hold cursors open across transac­
           tions--for example, if you use one session for your
           long lifespan cursors (typically read-only) and
           another for your short update transactions.

           For compatibility with old DBI scripts, the driver can
           be specified by passing its name as the fourth argu­
           ment to `connect' (instead of `\%attr'):

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

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

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

           `connect_cached' is like the connect entry elsewhere
           in this document, except that the database handle
           returned is also stored in a hash associated with the

           nect_cached' with the same parameter values, then the
           corresponding cached `$dbh' will be returned if it is
           still valid.  The cached database handle is replaced
           with a new connection if it has been disconnected or
           if the `ping' method fails.

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

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

           The cache can be accessed (and cleared) via the the
           CachedKids entry elsewhere in this document 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.

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

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

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

           Data sources are returned in a form suitable for pass­
           ing to the the connect entry elsewhere in this docu­
           ment method (that is, they will include the
           "`dbi:$driver:'" prefix).

           Note that many drivers have no way of knowing what
           data sources might be available for it. These drivers
           return an empty or incomplete list or may require

           database handle, to be supplied.

       `trace'
             DBI->trace($trace_level)
             DBI->trace($trace_level, $trace_filename)

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

           Trace levels are as follows:

             0 - Trace disabled.
             1 - Trace DBI method calls returning with results or errors.
             2 - Trace method entry with parameters and returning with results.
             3 - As above, adding some high-level information from the driver
                 and some internal information from the DBI.
             4 - As above, adding more detailed information from the driver.
                 Also includes DBI mutex information when using threaded Perl.
             5 and above - As above but with more and more obscure information.

           Trace level 1 is best for a simple overview of what's
           happening.  Trace level 2 is a good choice for general
           purpose tracing.  Levels 3 and above (up to 9) are
           best reserved for investigating a specific problem,
           when you need to see "inside" the driver and DBI.

           The trace output is detailed and typically very use­
           ful. Much of the trace output is formatted using the
           the neat entry elsewhere in this document function, so
           strings in the trace output may be edited and trun­
           cated.

           Initially trace output is written to `STDERR'.  If
           `$trace_filename' is specified and can be opened in
           append mode then all trace output (including that from
           other handles) is redirected to that file.  A warning
           is generated is the file can't be opened.  Further
           calls to `trace' without a `$trace_filename' do not
           alter where the trace output is sent. If `$trace_file­
           name' is undefined, then trace output is sent to
           `STDERR' and the previous trace file is closed.  The
           `trace' method returns the previous tracelevel.

           See also the `$h-'>`trace' and `$h-'>`trace_msg' meth­
           ods and the the DEBUGGING entry elsewhere in this doc­
           ument section for information about the `DBI_TRACE'
           environment variable.


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

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

           Return a string containing a neat (and tidy) represen­
           tation of the supplied value.

           Strings will be quoted, although internal quotes will
           not be escaped.  Values known to be numeric will be
           unquoted. Undefined (NULL) values will be shown as
           `undef' (without quotes). Unprintable characters will
           be replaced by dot (.).

           For result strings longer than `$maxlen' the result
           string will be truncated to `$maxlen-4' and "`...''"
           will be appended.  If `$maxlen' is 0 or `undef', it
           defaults to `$DBI::neat_maxlen' which, in turn,
           defaults to 400.

           This function is designed to format values for human
           consumption.  It is used internally by the DBI for the
           trace entry elsewhere in this document output. It
           should typically not be used for formatting values for
           database use.  (See also the quote entry elsewhere in
           this document.)

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

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

       `looks_like_number'
             @bool = DBI::looks_like_number(@array);

           Returns true for each element that looks like a num­
           ber.  Returns false for each element that does not
           look like a number.  Returns `undef' for each element
           that is undefined or empty.

       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.

       but they do have limitations. Specifically, they have a
       short lifespan: because they are associated with the last
       handle used, they should only be used immediately after
       calling the method that "sets" them.  If in any doubt, use
       the corresponding method call.

       `$DBI::err'
           Equivalent to `$h-'>`err'.

       `$DBI::errstr'
           Equivalent to `$h-'>`errstr'.

       `$DBI::state'
           Equivalent to `$h-'>`state'.

       `$DBI::rows'
           Equivalent to `$h-'>`rows'. Please refer to the docu­
           mentation for the the rows entry elsewhere in this
           document method.

       `$DBI::lasth'
           Returns the DBI object handle used for the most recent
           DBI method call.  If the last DBI method call was a
           DESTROY then $DBI::lasth will return the handle of the
           parent of the destroyed handle, if there is one.


METHODS COMMON TO ALL HANDLES

       The following methods can be used by all types of DBI han­
       dles.

       `err'
             $rv = $h->err;

           Returns the native database engine error code from the
           last driver method called. The code is typically an
           integer but you should not assume that.

           The DBI resets $h->err to undef before most DBI method
           calls, so the value only has a short lifespan. Also,
           most drivers share the same error variables across all
           their handles, so calling a method on one handle will
           typically reset the error on all the other handles
           that are children of that driver.

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

       `errstr'
             $str = $h->errstr;

           the last driver method called. This has the same
           lifespan issues as the the err entry elsewhere in this
           document method described above.

       `state'
             $str = $h->state;

           Returns an error code in the standard SQLSTATE five
           character format.  Note that the specific success code
           `00000' is translated to '' (false). If the driver
           does not support SQLSTATE (and most don't), then state
           will return `S1000' (General Error) for all errors.

           The driver is free to return any value via `state',
           e.g., warning codes, even if it has not declared an
           error by returning a true value via the the err entry
           elsewhere in this document method described above.

       `trace'
             $h->trace($trace_level);
             $h->trace($trace_level, $trace_filename);

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

           Trace level 1 is best for a simple overview of what's
           happening.  Trace level 2 is a good choice for general
           purpose tracing.  Levels 3 and above (up to 9) are
           best reserved for investigating a specific problem,
           when you need to see "inside" the driver and DBI.  Set
           `$trace_level' to 0 to disable the trace.

           The trace output is detailed and typically very use­
           ful. Much of the trace output is formatted using the
           the neat entry elsewhere in this document function, so
           strings in the trace output may be edited and trun­
           cated.

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

           See also the `DBI-'>`trace' method and the DEBUGGING
           entry elsewhere in this document for information about
           the `DBI_TRACE' environment variable.

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

           Writes `$message_text' to the trace file if trace is
           enabled for `$h' or for the DBI as a whole. Can also
           be called as `DBI-'>`trace_msg($msg)'.  See the trace
           entry elsewhere in this document.

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

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

           The `func' method can be used to call private non-
           standard and non-portable methods implemented by the
           driver. Note that the function name is given as the
           last argument.

           This method is not directly related to calling stored
           procedures.  Calling stored procedures is currently
           not defined by the DBI.  Some drivers, such as
           DBD::Oracle, support it in non-portable ways.  See
           driver documentation for more details.


ATTRIBUTES COMMON TO ALL HANDLES

       These attributes are common to all types of DBI handles.

       Some attributes are inherited by child handles. That is,
       the value of an inherited attribute in a newly created
       statement handle is the same as the value in the parent
       database handle. Changes to attributes in the new state­
       ment handle do not affect the parent database handle and
       changes to the database handle do not affect existing
       statement handles, only future ones.

       Attempting to set or get the value of an unknown attribute
       is fatal, except for private driver specific attributes
       (which all have names starting with a lowercase letter).

       Example:

         $h->{AttributeName} = ...;    # set/write
         ... = $h->{AttributeName};    # get/read

       `Warn' (boolean, inherited)
           Enables useful warnings for certain bad practices.
           Enabled by default. Some emulation layers, especially
           those for Perl 4 interfaces, disable warnings.  Since
           warnings are generated using the Perl `warn' function,
           they can be intercepted using the Perl


       `Active' (boolean, read-only)
           True if the handle object is "active". This is rarely
           used in applications. The exact meaning of active is
           somewhat vague at the moment. For a database handle it
           typically means that the handle is connected to a
           database (`$dbh-'>`disconnect' sets `Active' off).
           For a statement handle it typically means that the
           handle is a `SELECT' that may have more data to fetch.
           (Fetching all the data or calling `$sth-'>`finish'
           sets `Active' off.)

       `Kids' (integer, read-only)
           For a driver handle, `Kids' is the number of currently
           existing database handles that were created from that
           driver handle.  For a database handle, `Kids' is the
           number of currently existing statement handles that
           were created from that database handle.

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

       `CachedKids' (hash ref)
           For a database handle, returns a reference to the
           cache (hash) of statement handles created by the the
           prepare_cached entry elsewhere in this document
           method.  For a driver handle, returns a reference to
           the cache (hash) of database handles created by the
           the connect_cached entry elsewhere in this document
           method.

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

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

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

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


       `PrintError' (boolean, inherited)
           This attribute can be used to force errors to generate
           warnings (using `warn') in addition to returning error
           codes in the normal way.  When set "on", any method
           which results in an error occuring will cause the DBI
           to effectively do a `warn("$class $method failed:
           $DBI::errstr")' where `$class' is the driver class and
           `$method' is the name of the method which failed.
           E.g.,

             DBD::Oracle::db prepare failed: ... error text here ...

           By default, `DBI-'>`connect' sets `PrintError' "on".

           If desired, the warnings can be caught and processed
           using a `$SIG{__WARN__}' handler or modules like
           CGI::Carp and CGI::ErrorWrap.

       `RaiseError' (boolean, inherited)
           This attribute can be used to force errors to raise
           exceptions rather than simply return error codes in
           the normal way. It is "off" by default.  When set
           "on", any method which results in an error will cause
           the DBI to effectively do a `die("$class $method
           failed: $DBI::errstr")', where `$class' is the driver
           class and `$method' is the name of the method that
           failed. E.g.,

             DBD::Oracle::db prepare failed: ... error text here ...

           If you turn `RaiseError' on then you'd normally turn
           `PrintError' off.  If `PrintError' is also on, then
           the `PrintError' is done first (naturally).

           Typically `RaiseError' is used in conjunction with
           `eval { ... }' to catch the exception that's been
           thrown and followed by an `if ($@) { ... }' 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

           exited.  The same logic applies to other attributes,
           including `PrintError'.

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

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

       `ChopBlanks' (boolean, inherited)
           This attribute can be used to control the trimming of
           trailing space characters from fixed width character
           (CHAR) fields. No other field types are affected, even
           where field values have trailing spaces.

           The default is false (although it is possible that the
           default may change).  Applications that need specific
           behavior should set the attribute as needed. Emulation
           interfaces should set the attribute to match the
           behavior of the interface they are emulating.

           Drivers are not required to support this attribute,
           but any driver which does not support it must arrange
           to return `undef' as the attribute value.

       `LongReadLen' (unsigned integer, inherited)
           This attribute may be used to control the maximum
           length of long fields ("blob", "memo", etc.) which the
           driver will read from the database automatically when
           it fetches each row of data.  The `LongReadLen'
           attribute only relates to fetching and reading long
           values; it is not involved in inserting or updating
           them.

           A value of 0 means not to automatically fetch any long
           data. (`fetch' should return `undef' for long fields
           when `LongReadLen' is 0.)

           The default is typically 0 (zero) bytes but may vary
           between drivers.  Applications fetching long fields
           should set this value to slightly larger than the
           longest long field value to be fetched.

           Some databases return some long types encoded as pairs

           to the underlying data length and not the doubled-up
           length of the encoded string.

           Changing the value of `LongReadLen' for a statement
           handle after it has been `prepare''d will typically
           have no effect, so it's common to set `LongReadLen' on
           the `$dbh' before calling `prepare'.

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

           See the LongTruncOk entry elsewhere in this document
           for more information on truncation behavior.

       `LongTruncOk' (boolean, inherited)
           This attribute may be used to control the effect of
           fetching a long field value which has been truncated
           (typically because it's longer than the value of the
           `LongReadLen' attribute).

           By default, `LongTruncOk' is false and so fetching a
           long value that needs to be truncated will cause the
           fetch to fail.  (Applications should always be sure to
           check for errors after a fetch loop in case an error,
           such as a divide by zero or long field truncation,
           caused the fetch to terminate prematurely.)

           If a fetch fails due to a long field truncation when
           `LongTruncOk' is false, many drivers will allow you to
           continue fetching further rows.

           See also the LongReadLen entry elsewhere in this docu­
           ment.

       `Taint' (boolean, inherited)
           If this attribute is set to a true value and Perl is
           running in taint mode (e.g., started with the `-T'
           option), then all data fetched from the database is
           tainted, and the arguments to most DBI method calls
           are checked for being tainted. This may change.

           The attribute defaults to off, even if Perl is in
           taint mode.  See the perlsec manpage for more about
           taint mode.  If Perl is not running in taint mode,
           this attribute has no effect.

           When fetching data that you trust you can turn off the
           Taint attribute, for that statement handle, for the
           duration of the fetch loop.

           Currently only fetched data is tainted. It is possible
           that the results of other DBI method calls, and the

           future versions. That change may well break your
           applications unless you take great care now. If you
           use DBI Taint mode, please report your experience and
           any suggestions for changes.

       `private_*'
           The DBI provides a way to store extra information in a
           DBI handle as "private" attributes. The DBI will allow
           you to store and retreive any attribute which has a
           name starting with "`private_'". It is strongly recom­
           mended 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_YourFullMod­
           uleName_thingy'").


DBI DATABASE HANDLE OBJECTS

       This section covers the methods and attributes associated
       with database handles.

       Database Handle Methods

       The following methods are specified for DBI database han­
       dles:

       `do'
             $rc  = $dbh->do($statement)           or die $dbh->errstr;
             $rc  = $dbh->do($statement, \%attr)   or die $dbh->errstr;
             $rv  = $dbh->do($statement, \%attr, @bind_values) or ...

           Prepare and execute a single statement. Returns the
           number of rows affected or `undef' on error. A return
           value of `-1' means the number of rows is not known or
           is not available.

           This method is typically most useful for non-`SELECT'
           statements that either cannot be prepared in advance
           (due to a limitation of the driver) or do not need to
           be executed repeatedly. It should not be used for
           `SELECT' statements because it does not return a
           statement handle (so you can't fetch any data).

           The default `do' method is logically similar to:

             sub do {
                 my($dbh, $statement, $attr, @bind_values) = @_;
                 my $sth = $dbh->prepare($statement, $attr) or return undef;
                 $sth->execute(@bind_values) or return undef;
                 my $rows = $sth->rows;
                 ($rows == 0) ? "0E0" : $rows; # always return true if no error
             }

           For example:

                 DELETE FROM table
                 WHERE status = ?
             }, undef, 'DONE') or die $dbh->errstr;

           Using placeholders and `@bind_values' with the `do'
           method can be useful because it avoids the need to
           correctly quote any variables in the `$statement'. But
           if you'll be executing the statement many times then
           it's more efficient to `prepare' it once and call
           `execute' many times instead.

           The `q{...}' style quoting used in this example avoids
           clashing with quotes that may be used in the SQL
           statement. Use the double-quote-like `qq{...}' opera­
           tor if you want to interpolate variables into the
           string.  See the Quote and Quote-like Operators entry
           in the perlop manpage for more details.

       `selectrow_array'
             @row_ary = $dbh->selectrow_array($statement);
             @row_ary = $dbh->selectrow_array($statement, \%attr);
             @row_ary = $dbh->selectrow_array($statement, \%attr, @bind_values);

           This utility method combines the prepare, execute, and
           fetchrow_array entries elsewhere in this document into
           a single call. If called in a list context, it returns
           the first row of data from the statement. If called in
           a scalar context, it returns the first field of the
           first row. The `$statement' parameter can be a previ­
           ously prepared statement handle, in which case the
           `prepare' is skipped.

           If any method fails, and the RaiseError entry else­
           where in this document is not set, `selectrow_array'
           will return an empty list.

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

       `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 the prepare, execute, and
           fetchall_arrayref entries elsewhere in this document
           into a single call. It returns a reference to an array
           containing a reference to an array for each row of


           The `$statement' parameter can be a previously pre­
           pared statement handle, in which case the `prepare' is
           skipped. This is recommended if the statement is going
           to be executed many times.

           If the RaiseError entry elsewhere in this document 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 it has been fetched thus far. $DBI::err
           should be checked to catch that.

       `selectall_hashref'
             $ary_ref = $dbh->selectall_hashref($statement);
             $ary_ref = $dbh->selectall_hashref($statement, \%attr);
             $ary_ref = $dbh->selectall_hashref($statement, \%attr, @bind_values);

           This utility method combines the prepare, execute, and
           fetchrow_hashref entries elsewhere in this document
           into a single call. It returns a reference to an array
           containing, for each row of data fetched, a reference
           to a hash containing field name and value pairs for
           that row.

           The `$statement' parameter can be a previously pre­
           pared 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 the
           RaiseError entry elsewhere in this document is not
           set, `selectall_hashref' will return `undef'.  If
           `fetchrow_hashref' fails and the RaiseError entry
           elsewhere in this document 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 the prepareand execute
           entries elsewhere in this document, and fetching one
           column from all the rows, into a single call. It
           returns a reference to an array containing the values
           of the first column from each row.

           The `$statement' parameter can be a previously pre­
           pared statement handle, in which case the `prepare' is
           skipped. This is recommended if the statement is going
           to be executed many times.

           entry elsewhere in this document is not set, `select­
           col_arrayref' will return `undef'.  If `fetch' fails
           and the RaiseError entry elsewhere in this document is
           not set, then it will return with whatever data it has
           fetched thus far. $DBI::err should be checked to catch
           that.

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

           Prepares a single statement for later execution by the
           database engine and returns a reference to a statement
           handle object.

           The returned statement handle can be used to get
           attributes of the statement and invoke the the execute
           entry elsewhere in this document method. See the
           Statement Handle Methods entry elsewhere in this docu­
           ment.

           Drivers for engines without the concept of preparing a
           statement will typically just store the statement in
           the returned handle and process it when `$sth-'>`exe­
           cute' is called. Such drivers are unlikely to give
           much useful information about the statement, such as
           `$sth-'>`{NUM_OF_FIELDS}', until after `$sth-'>`exe­
           cute' has been called. Portable applications should
           take this into account.

           In general, DBI drivers do not parse the contents of
           the statement (other than simply counting any the
           Placeholders entry elsewhere in this document). The
           statement is passed directly to the database engine,
           sometimes known as pass-thru mode. This has advantages
           and disadvantages. On the plus side, you can access
           all the functionality of the engine being used. On the
           downside, you're limited if you're using a simple
           engine, and you need to take extra care if writing
           applications intended to be portable between engines.

           Portable applications should not assume that a new
           statement can be prepared and/or executed while still
           fetching results from a previous statement.

           Some command-line SQL tools use statement terminators,
           like a semicolon, to indicate the end of a statement.
           Such terminators should not normally be used with the
           DBI.

       `prepare_cached'

             $sth = $dbh->prepare_cached($statement, \%attr)
             $sth = $dbh->prepare_cached($statement, \%attr, $allow_active)

           Like the prepare entry elsewhere in this document
           except that the statement handle returned will be
           stored in a hash associated with the `$dbh'. If
           another call is made to `prepare_cached' with the same
           `$statement' and `%attr' values, then the correspond­
           ing cached `$sth' will be returned without contacting
           the database server.

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

           Here's an example of one possible use of `pre­
           pare_cached':

             while ( ($field, $value) = each %search_fields ) {
                 push @sql,   "$field = ?";
                 push @values, $value;
             }
             $qualifier = "";
             $qualifier = "where ".join(" and ", @sql) if @sql;
             $sth = $dbh->prepare_cached("SELECT * FROM table $qualifier");
             $sth->execute(@values);

       `commit'
             $rc  = $dbh->commit     or die $dbh->errstr;

           Commit (make permanent) the most recent series of
           database changes if the database supports transactions
           and AutoCommit is off.

           If `AutoCommit' is on, then calling `commit' will
           issue a "commit ineffective with AutoCommit" warning.

           See also the Transactions entry elsewhere in this doc­
           ument in the the FURTHER INFORMATION entry elsewhere
           in this document 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


           If `AutoCommit' is on, then calling `rollback' will
           issue a "rollback ineffective with AutoCommit" warn­
           ing.

           See also the Transactions entry elsewhere in this doc­
           ument in the the FURTHER INFORMATION entry elsewhere
           in this document section below.

       `disconnect'
             $rc = $dbh->disconnect  or warn $dbh->errstr;

           Disconnects the database from the database handle.
           `disconnect' is typically only used before exiting the
           program. The handle is of little use after disconnect­
           ing.

           The transaction behavior of the `disconnect' method
           is, sadly, undefined.  Some database systems (such as
           Oracle and Ingres) will automatically commit any out­
           standing changes, but others (such as Informix) will
           rollback any outstanding changes.  Applications not
           using `AutoCommit' should explicitly call `commit' or
           `rollback' before calling `disconnect'.

           The database is automatically disconnected by the
           `DESTROY' method if still connected when there are no
           longer any references to the handle.  The `DESTROY'
           method for each driver should implicitly call `roll­
           back' to undo any uncommitted changes. This is vital
           behavior to ensure that incomplete transactions don't
           get committed simply because Perl calls `DESTROY' on
           every object before exiting. Also, do not rely on the
           order of object destruction during "global destruc­
           tion", as it is undefined.

           Generally, if you want your changes to be commited or
           rolled back when you disconnect, then you should
           explicitly call the commit entry elsewhere in this
           document or the rollback entry elsewhere in this docu­
           ment before disconnecting.

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

       `ping'
             $rc = $dbh->ping;

           Attempts to determine, in a reasonably efficient way,
           if the database server is still running and the

           should implement this function in the most suitable
           manner for their database engine.

           The current default implementation always returns true
           without actually doing anything. Actually, it returns
           "`0 but true'" which is true but zero. That way you
           can tell if the return value is genuine or just the
           default. Drivers should override this method with one
           that does the right thing for their type of database.

           Few applications would have direct use for this
           method. See the specialized Apache::DBI module for one
           example usage.

       `table_info' NEW
           Warning: This method is experimental and may change.

             $sth = $dbh->table_info;
             $sth = $dbh->table_info( \%attr );

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

           The following attributes (all or separate) may be used
           as selection criteria:

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

           Note: The support for the selection criteria is driver
           specific. If the driver doesn't support one or more
           then them then you'll get back more than you asked for
           and can do the filtering yourself.

           The arguments TABLE_CAT, TABLE_SCHEM and TABLE_NAME
           may accept search patterns according to the
           database/driver, for example:

             $sth = $dbh->table_info( { TABLE_NAME  => '%TAB%'} );

           The value of TABLE_TYPE is a comma-separated list of
           one or more types of tables to be returned in the
           result set. Each value may optionally be quoted, e.g.:

             $sth = $dbh->table_info( { TABLE_TYPE  => "TABLE" } );
             $sth = $dbh->table_info( { TABLE_TYPE  => "'TABLE', 'VIEW'" } );

           In addition the following special cases may also be


           · If the value of TABLE_CAT is '%' and TABLE_SCHEM and
               TABLE_NAME name are empty strings, the result set
               contains a list of catalog names. For example:
                 $sth = $dbh->table_info({ TABLE_CAT=>'%', TABLE_SCHEM=>'', TABLE_NAME=>'' });

           · If the value of TABLE_SCHEM is '%' and TABLE_CAT and
               TABLE_NAME are empty strings, the result set
               contains a list of schema names.

           · If the value of TABLE_TYPE is '%' and TABLE_CAT,
               TABLE_SCHEM, and TABLE_NAME are all empty strings,
               the result set contains a list of table types.

           The statement handle returned has at least the follow­
           ing fields in the order show below. Other fields,
           after these, may also be present.

           TABLE_CAT: Table catalog identifier. This field is
           NULL (`undef') if not applicable to the data source,
           which is usually the case. This field is empty if not
           applicable to the table.

           TABLE_SCHEM: The name of the schema containing the
           TABLE_NAME value.  This field is NULL (`undef') if not
           applicable to data source, and empty if not applicable
           to the table.

           TABLE_NAME: Name of the table (or view, synonym, etc).

           TABLE_TYPE: One of the following: "TABLE", "VIEW",
           "SYSTEM TABLE", "GLOBAL TEMPORARY", "LOCAL TEMPORARY",
           "ALIAS", "SYNONYM" or a type identifier that is spe­
           cific to the data source.

           REMARKS: A description of the table. May be NULL
           (`undef').

           Note that `table_info' might not return records for
           all tables.  Applications can use any valid table
           regardless of whether it's returned by `table_info'.
           See also the tables entry elsewhere in this document.

           For more detailed information about the fields and
           their meanings, you can refer to:

             http://msdn.microsoft.com/library/psdk/dasdk/odch6wqb.htm

           If that URL ceases to work then use the MSDN search
           facility at:

             http://search.microsoft.com/us/dev/

           phrase option.  The link you want will probably just
           be called `SQLTables' and will be part of the Data
           Access SDK.

           See also page 306 of the (very large) SQL/CLI specifi­
           cation:

             http://www.jtc1sc32.org/sc32/jtc1sc32.nsf/Attachments/DF86E81BE70151D58525699800643F56/$FILE/32N0595T.PDF

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

             @names = $dbh->tables;
             @names = $dbh->tables( \%attr );

           Returns a list of table and view names, possibly
           including a schema prefix.  This list should include
           all tables that can be used in a `SELECT' statement
           without further qualification.

           Note that `table_info' might not return records for
           all tables.  Applications can use any valid table
           regardless of whether it's returned by tables.  See
           also the table_info entry elsewhere in this document.

       `type_info_all' NEW
           Warning: This method is experimental and may change.

             $type_info_all = $dbh->type_info_all;

           Returns a reference to an array which holds informa­
           tion about each data type variant supported by the
           database and driver. The array and its contents should
           be treated as read-only.

           The first item is a reference to an 'index' hash of
           `Name ='> `Index' pairs.  The items following that are
           references to arrays, one per supported data type
           variant. The leading index hash defines the names and
           order of the fields within the arrays that follow it.
           For example:

               {   TYPE_NAME         => 0,
                   DATA_TYPE         => 1,
                   COLUMN_SIZE       => 2,     # was PRECISION originally
                   LITERAL_PREFIX    => 3,
                   LITERAL_SUFFIX    => 4,
                   CREATE_PARAMS     => 5,
                   NULLABLE          => 6,
                   CASE_SENSITIVE    => 7,
                   SEARCHABLE        => 8,
                   UNSIGNED_ATTRIBUTE=> 9,
                   FIXED_PREC_SCALE  => 10,    # was MONEY originally
                   AUTO_UNIQUE_VALUE => 11,    # was AUTO_INCREMENT originally
                   LOCAL_TYPE_NAME   => 12,
                   MINIMUM_SCALE     => 13,
                   MAXIMUM_SCALE     => 14,
                   NUM_PREC_RADIX    => 15,
               },
               [ 'VARCHAR', SQL_VARCHAR,
                   undef, "'","'", undef,0, 1,1,0,0,0,undef,1,255, undef
               ],
               [ 'INTEGER', SQL_INTEGER,
                   undef,  "", "", undef,0, 0,1,0,0,0,undef,0,  0, 10
               ],
             ];

           Note that more than one row may have the same value in
           the `DATA_TYPE' field if there are different ways to
           spell the type name and/or there are variants of the
           type with different attributes (e.g., with and without
           `AUTO_UNIQUE_VALUE' set, with and without
           `UNSIGNED_ATTRIBUTE', etc).

           The rows are ordered by `DATA_TYPE' first and then by
           how closely each type maps to the corresponding ODBC
           SQL data type, closest first.

           The meaning of the fields is described in the documen­
           tation for the the type_info entry elsewhere in this
           document method. The index values shown above (e.g.,
           `NULLABLE ='> `6') are for illustration only. Drivers
           may define the fields with a different order.

           This method is not normally used directly. The the
           type_info entry elsewhere in this document method pro­
           vides a more useful interface to the data.

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

           driver-specific columns of information - though it's
           recommended that they start at column index 50 to
           leave room for expansion of the DBI/ODBC specifica­
           tion.

       `type_info' NEW
           Warning: This method is experimental and may change.

             @type_info = $dbh->type_info($data_type);

           Returns a list of hash references holding information
           about one or more variants of `$data_type'. The list
           is ordered by `DATA_TYPE' first and then by how
           closely each type maps to the corresponding ODBC SQL
           data type, closest first.  If called in a scalar con­
           text then only the first (best) element is returned.

           If `$data_type' is undefined or `SQL_ALL_TYPES', then
           the list will contain hashes for all data type vari­
           ants supported by the database and driver.

           If `$data_type' is an array reference then `type_info'
           returns the information for the first type in the
           array that has any matches.

           The keys of the hash follow the same letter case con­
           ventions as the rest of the DBI (see the Naming Con­
           ventions and Name Space entry elsewhere in this docu­
           ment). The following items should exist:

           TYPE_NAME (string)
               Data type name for use in CREATE TABLE statements
               etc.

           DATA_TYPE (integer)
               SQL data type number.

           COLUMN_SIZE (integer)
               For numeric types, this is either the total number
               of digits (if the NUM_PREC_RADIX value is 10) or
               the total number of bits allowed in the column (if
               NUM_PREC_RADIX is 2).

               For string types, this is the maximum size of the
               string in bytes.

               For date and interval types, this is the maximum
               number of characters needed to display the value.

           LITERAL_PREFIX (string)
               Characters used to prefix a literal. A typical
               prefix is "`''" for characters, or possibly "`0x'"
               for binary values passed as hexadecimal.  NULL

               this is not applicable.

           LITERAL_SUFFIX (string)
               Characters used to suffix a literal. Typically
               "`''" for characters.  NULL (`undef') is returned
               for data types where this is not applicable.

           CREATE_PARAMS (string)
               Parameter names for data type definition. For
               example, `CREATE_PARAMS' for a `DECIMAL' would be
               "`precision,scale'" if the DECIMAL type should be
               declared as `DECIMAL('precision,scale`)' where
               precision and scale are integer values.  For a
               `VARCHAR' it would be "`max length'".  NULL
               (`undef') is returned for data types for which
               this is not applicable.

           NULLABLE (integer)
               Indicates whether the data type accepts a NULL
               value: `0' or an empty string = no, `1' = yes, `2'
               = unknown.

           CASE_SENSITIVE (boolean)
               Indicates whether the data type is case sensitive
               in collations and comparisons.

           SEARCHABLE (integer)
               Indicates how the data type can be used in a WHERE
               clause, as follows:

                 0 - Cannot be used in a WHERE clause
                 1 - Only with a LIKE predicate
                 2 - All comparison operators except LIKE
                 3 - Can be used in a WHERE clause with any comparison operator

           UNSIGNED_ATTRIBUTE (boolean)
               Indicates whether the data type is unsigned.  NULL
               (`undef') is returned for data types for which
               this is not applicable.

           FIXED_PREC_SCALE (boolean)
               Indicates whether the data type always has the
               same precision and scale (such as a money type).
               NULL (`undef') is returned for data types for
               which this is not applicable.

           AUTO_UNIQUE_VALUE (boolean)
               Indicates whether a column of this data type is
               automatically set to a unique value whenever a new
               row is inserted.  NULL (`undef') is returned for
               data types for which this is not applicable.

               Localized version of the `TYPE_NAME' for use in
               dialog with users.  NULL (`undef') is returned if
               a localized name is not available (in which case
               `TYPE_NAME' should be used).

           MINIMUM_SCALE (integer)
               The minimum scale of the data type. If a data type
               has a fixed scale, then `MAXIMUM_SCALE' holds the
               same value.  NULL (`undef') is returned for data
               types for which this is not applicable.

           MAXIMUM_SCALE (integer)
               The maximum scale of the data type. If a data type
               has a fixed scale, then `MINIMUM_SCALE' holds the
               same value.  NULL (`undef') is returned for data
               types for which this is not applicable.

           SQL_DATA_TYPE (integer)
               This column is the same as the `DATA_TYPE' column,
               except for interval and datetime data types.  For
               interval and datetime data types, the
               `SQL_DATA_TYPE' field will return `SQL_INTERVAL'
               or `SQL_DATETIME', and the `SQL_DATETIME_SUB'
               field below will return the subcode for the spe­
               cific interval or datetime data type. If this
               field is NULL, then the driver does not support or
               report on interval or date subtypes.

           SQL_DATETIME_SUB (integer)
               For interval or datetime data types, where the
               `SQL_DATA_TYPE' field above is `SQL_INTERVAL' or
               `SQL_DATETIME', this field will hold the subcode
               for the specific interval or datetime data type.
               Otherwise it will be NULL (`undef').

           NUM_PREC_RADIX (integer)
               The radix value of the data type. For approximate
               numeric types, `NUM_PREC_RADIX' contains the value
               2 and `COLUMN_SIZE' holds the number of bits. For
               exact numeric types, `NUM_PREC_RADIX' contains the
               value 10 and `COLUMN_SIZE' holds the number of
               decimal digits. NULL (`undef') is returned either
               for data types for which this is not applicable or
               if the driver cannot report this information.

           INTERVAL_PRECISION (integer)
               The interval leading precision for interval types.
               NULL is returned either for data types for which
               this is not applicable or if the driver cannot
               report this information.

           For example, to find the type name for the fields in a
           select statement you can do:


           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.

           For more detailed information about these fields and
           their meanings, you can refer to:

             http://msdn.microsoft.com/library/psdk/dasdk/odch6yy7.htm

           If that URL ceases to work then use the MSDN search
           facility at

               http://search.microsoft.com/us/dev/

           and search the MSDN Library for `SQLGetTypeInfo
           returns' using the exact phrase option.  The link you
           want will probably just be called `SQLGetTypeInfo'
           (there may be more than one).

           The individual data types are currently described
           here:

             http://msdn.microsoft.com/library/psdk/dasdk/odap8fcj.htm

           If that URL ceases to work, or to get more general
           information, use the MSDN search facility as described
           above and search for `SQL Data Types'.

       `quote'
             $sql = $dbh->quote($value);
             $sql = $dbh->quote($value, $data_type);

           Quote a string literal for use as a literal value in
           an SQL statement, by escaping any special characters
           (such as quotation marks) contained within the string
           and adding the required type of outer quotation marks.

             $sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
                           $dbh->quote("Don't");

           For most database types, quote would return `'Don''t''
           (including the outer quotation marks).

           An undefined `$value' value will be returned as the
           string `NULL' (without quotation marks) to match how


           If `$data_type' is supplied, it is used to try to
           determine the required quoting behavior by using the
           information returned by the type_info entry elsewhere
           in this document.  As a special case, the standard
           numeric types are optimized to return `$value' without
           calling `type_info'.

           Quote will probably not be able to deal with all pos­
           sible input (such as binary data or data containing
           newlines), and is not related in any way with escaping
           or quoting shell meta-characters. There is no need to
           quote values being used with the Placeholders and Bind
           Values entry elsewhere in this document.

       Database Handle Attributes

       This section describes attributes specific to database
       handles.

       Changes to these database handle attributes do not affect
       any other existing or future database handles.

       Attempting to set or get the value of an unknown attribute
       is fatal, except for private driver-specific attributes
       (which all have names starting with a lowercase letter).

       Example:

         $h->{AutoCommit} = ...;       # set/write
         ... = $h->{AutoCommit};       # get/read

       `AutoCommit'  (boolean)
           If true, then database changes cannot be rolled-back
           (undone).  If false, then database changes automati­
           cally occur within a "transaction", which must either
           be committed or rolled back using the `commit' or
           `rollback' methods.

           Drivers should always default to `AutoCommit' mode (an
           unfortunate choice largely forced on the DBI by ODBC
           and JDBC conventions.)

           Attempting to set `AutoCommit' to an unsupported value
           is a fatal error.  This is an important feature of the
           DBI. Applications that need full transaction behavior
           can set `$dbh-'>`{AutoCommit} = 0' (or set `AutoCom­
           mit' to 0 via the connect entry elsewhere in this doc­
           ument) without having to check that the value was
           assigned successfully.

           For the purposes of this description, we can divide


             Databases which don't support transactions at all.
             Databases in which a transaction is always active.
             Databases in which a transaction must be explicitly started (C<'BEGIN WORK'>).

           * Databases which don't support transactions at all

           For these databases, attempting to turn `AutoCommit'
           off is a fatal error.  `commit' and `rollback' both
           issue warnings about being ineffective while `AutoCom­
           mit' is in effect.

           * Databases in which a transaction is always active

           These are typically mainstream commercial relational
           databases with "ANSI standard" transaction behavior.
           If `AutoCommit' is off, then changes to the database
           won't have any lasting effect unless the commit entry
           elsewhere in this document is called (but see also the
           disconnect entry elsewhere in this document). If the
           rollback entry elsewhere in this document is called
           then any changes since the last commit are undone.

           If `AutoCommit' is on, then the effect is the same as
           if the DBI called `commit' automatically after every
           successful database operation. In other words, calling
           `commit' or `rollback' explicitly while `AutoCommit'
           is on would be ineffective because the changes would
           have already been commited.

           Changing `AutoCommit' from off to on should issue a
           the commit entry elsewhere in this document in most
           drivers.

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

           For databases which don't support a specific auto-com­
           mit mode, the driver has to commit each statement
           automatically using an explicit `COMMIT' after it com­
           pletes successfully (and roll it back using an
           explicit `ROLLBACK' if it fails).  The error informa­
           tion reported to the application will correspond to
           the statement which was executed, unless it succeeded
           and the commit or rollback failed.

           * Databases in which a transaction must be explicitly
           started

           For these databases, the intention is to have them act
           like databases in which a transaction is always active
           (as described above).

           transaction when `AutoCommit' is turned off (from the
           default "on" state) and will automatically begin
           another transaction after a the commit entry elsewhere
           in this document or the rollback entry elsewhere in
           this document.  In this way, the application does not
           have to treat these databases as a special case.

           See the commit, disconnect, and Transactions entries
           elsewhere in this document for other important notes
           about transactions.

       `Driver'  (handle)
           Holds the handle of the parent driver. The only recom­
           mended use for this is to find the name of the driver
           using:

             $dbh->{Driver}->{Name}

       `Name'  (string)
           Holds the "name" of the database. Usually (and recom­
           mended to be) the same as the "`dbi:DriverName:...'"
           string used to connect to the database, but with the
           leading "`dbi:DriverName:'" removed.

       `Statement'  (string, read-only)
           Returns the statement string passed to the most recent
           the prepare entry elsewhere in this document 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 setting `RowCacheSize' is
           ignored and getting the value returns `undef'.

           Some `RowCacheSize' values have special meaning, as
           follows:

             0 - Automatically determine a reasonable cache size for each C<SELECT>
             1 - Disable the local row cache
            >1 - Cache this many rows
            <0 - Cache as many rows that will fit into this much memory for each C<SELECT>.

           Note that large cache sizes may require a very large
           amount of memory (cached rows * maximum size of row).
           Also, a large cache will cause a longer delay not only
           for the first fetch, but also whenever the cache needs
           refilling.

           document statement handle attribute.


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'
             $rc = $sth->bind_param($p_num, $bind_value)  or die $sth->errstr;
             $rv = $sth->bind_param($p_num, $bind_value, \%attr)     or ...
             $rv = $sth->bind_param($p_num, $bind_value, $bind_type) or ...

           The `bind_param' method can be used to bind a value
           with a placeholder embedded in the prepared statement.
           Placeholders are indicated with question mark charac­
           ter (`?'). For example:

             $dbh->{RaiseError} = 1;        # save having to check each method call
             $sth = $dbh->prepare("SELECT name, age FROM people WHERE name LIKE ?");
             $sth->bind_param(1, "John%");  # placeholders are numbered from 1
             $sth->execute;
             DBI::dump_results($sth);

           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.  Undefined bind values or
           `undef' can be used to indicate null values.

           Some drivers do not support placeholders.

           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

           Data Types for Placeholders

           The `\%attr' parameter can be used to hint at the data

           driver is only interested in knowing if the place­
           holder should be bound as a number or a string.

             $sth->bind_param(1, $value, { TYPE => SQL_INTEGER });

           As a short-cut for this common case, the data type can
           be passed directly, in place of the `\%attr' hash ref­
           erence. 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 data type for a placeholder cannot be changed
           after the first `bind_param' call. However, it can be
           left unspecified, in which case it defaults to the
           previous value.

           The SQL_INTEGER and other related constants can be
           imported using

             use DBI qw(:sql_types);

           See the DBI Constants entry elsewhere in this document
           for more information.

           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.

           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 dif­
           ferent databases and is non-portable.

           See also the Placeholders and Bind Values entry else­
           where in this document for more information.

       `bind_param_inout'
             $rc = $sth->bind_param_inout($p_num, \$bind_value, $max_len)  or die $sth->errstr;
             $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, \%attr)     or ...
             $rv = $sth->bind_param_inout($p_num, \$bind_value, $max_len, $bind_type) or ...

           in this document, 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 the bind_param entry elsewhere in
           this document, the `$bind_value' variable is not read
           when `bind_param_inout' is called. Instead, the value
           in the variable is read at the time the execute entry
           elsewhere in this document is called.

           The additional `$max_len' parameter specifies the min­
           imum amount of memory to allocate to `$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.

           It is expected that few drivers will support this
           method. The only driver currently known to do so is
           DBD::Oracle (DBD::ODBC may support it in a future
           release). Therefore it should not be used for database
           independent applications.

           Undefined values or `undef' are used to indicate null
           values.  See also the Placeholders and Bind Values
           entry elsewhere in this document for more information.

       `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 successful `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.

           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 retreive the data after calling `execute'.

           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 effec­
           tively call the bind_param entry elsewhere in this
           document for each value before executing the state­
           ment.  Values bound in this way are usually treated as
           `SQL_VARCHAR' types unless the driver can determine
           the correct type (which is rare), or unless
           `bind_param' (or `bind_param_inout') has already been
           used to specify the type.

       `fetchrow_arrayref'
             $ary_ref = $sth->fetchrow_arrayref;
             $ary_ref = $sth->fetch;    # alias

           Fetches the next row of data and returns a reference
           to an array holding the field values.  Null fields are
           returned as `undef' values in the array.  This is the
           fastest way to fetch data, particularly if used with
           `$sth-'>`bind_columns'.

           If there are no more rows or if an error occurs, then
           `fetchrow_arrayref' returns an `undef'. You should
           check `$sth-'>`err' afterwards (or use the `RaiseEr­
           ror' attribute) to discover if the `undef' returned
           was due to an error.

           Note that the same array reference is returned for
           each fetch, so don't store the reference and then use
           it after a later fetch.  Also, the elements of the
           array are also reused for each row, so take care if
           you want to take a reference to an element. See also
           the bind_columns entry elsewhere in this document.

       `fetchrow_array'
            @ary = $sth->fetchrow_array;

           An alternative to `fetchrow_arrayref'. Fetches the
           next row of data and returns it as a list containing
           the field values.  Null fields are returned as `undef'
           values in the list.

           If there are no more rows or if an error occurs, then
           `fetchrow_array' returns an empty list. You should
           check `$sth-'>`err' afterwards (or use the `RaiseEr­
           ror' attribute) to discover if the empty list returned
           was due to an error.

           In a scalar context, `fetchrow_array' returns the
           value of the first field. An `undef' is returned if
           there are no more rows or if an error occurred. Since

           returned because the first field value was NULL, you
           should exercise some caution if you use
           `fetchrow_array' in a scalar context.

       `fetchrow_hashref'
            $hash_ref = $sth->fetchrow_hashref;
            $hash_ref = $sth->fetchrow_hashref($name);

           An alternative to `fetchrow_arrayref'. Fetches the
           next row of data and returns it as a reference to a
           hash containing field name and field value pairs.
           Null fields are returned as `undef' values in the
           hash.

           If there are no more rows or if an error occurs, then
           `fetchrow_hashref' returns an `undef'. You should
           check `$sth-'>`err' afterwards (or use the `RaiseEr­
           ror' attribute) to discover if the `undef' returned
           was due to an error.

           The optional `$name' parameter specifies the name of
           the statement handle attribute. For historical reasons
           it defaults to "`NAME'", however using either
           "`NAME_lc'" or "`NAME_uc'" is recomended for portabil­
           ity.

           The keys of the hash are the same names returned by
           `$sth-'>`{$name}'. If more than one field has the same
           name, there will only be one entry in the returned
           hash for those fields.

           Because of the extra work `fetchrow_hashref' and Perl
           have to perform, it is not as efficient as
           `fetchrow_arrayref' or `fetchrow_array'.

           Currently, a new hash reference is returned for each
           row.  This will change in the future to return the
           same hash ref each time, so don't rely on the current
           behaviour.

       `fetchall_arrayref'
             $tbl_ary_ref = $sth->fetchall_arrayref;
             $tbl_ary_ref = $sth->fetchall_arrayref( $slice_array_ref );
             $tbl_ary_ref = $sth->fetchall_arrayref( $slice_hash_ref  );

           The `fetchall_arrayref' method can be used to fetch
           all the data to be returned from a prepared and exe­
           cuted statement handle. It returns a reference to an
           array that contains one reference per row.

           If there are no rows to return, `fetchall_arrayref'
           returns a reference to an empty array. If an error
           occurs, `fetchall_arrayref' returns the data fetched

           `$sth-'>`err' afterwards (or use the `RaiseError'
           attribute) to discover if the data is complete or was
           truncated due to an error.

           When passed an array reference, `fetchall_arrayref'
           uses the fetchrow_arrayref entry elsewhere in this
           document to fetch each row as an array ref. If the
           parameter array is not empty then it is used as a
           slice to select individual columns by index number.

           With no parameters, `fetchall_arrayref' acts as if
           passed an empty array ref.

           When passed a hash reference, `fetchall_arrayref' uses
           the fetchrow_hashref entry elsewhere in this document
           to fetch each row as a hash reference. If the parame­
           ter hash is empty then fetchrow_hashref is simply
           called in a tight loop and the keys in the hashes have
           whatever name lettercase is returned by default from
           fetchrow_hashref.

           If the parameter hash is not empty, then it is used as
           a slice to select individual columns by name. The
           names should be lower case regardless of the letter
           case in `$sth-'>`{NAME}'.  The values of the hash
           should be set to 1.

           For example, to fetch just the first column of every
           row:

             $tbl_ary_ref = $sth->fetchall_arrayref([0]);

           To fetch the second to last and last column of every
           row:

             $tbl_ary_ref = $sth->fetchall_arrayref([-2,-1]);

           To fetch all fields of every row as a hash ref:

             $tbl_ary_ref = $sth->fetchall_arrayref({});

           To fetch only the fields called "foo" and "bar" of
           every row as a hash ref:

             $tbl_ary_ref = $sth->fetchall_arrayref({ foo=>1, bar=>1 });

           The first two examples return a reference to an array
           of array refs. The last returns a reference to an
           array of hash refs.

       `fetchall_hashref'
             $tbl_ary_ref = $sth->fetchall_hashref;

           the data to be returned from a prepared and executed
           statement handle. It returns a reference to an array
           that contains one hash of field name and value pairs
           per row.

           If there are no rows to return, `fetchall_hashref'
           returns a reference to an empty array. If an error
           occurs, `fetchall_hashref' returns the data fetched
           thus far, which may be none.  You should check
           `$sth-'>`err' afterwards (or use the `RaiseError'
           attribute) to discover if the data is complete or was
           truncated due to an error.

       `finish'
             $rc  = $sth->finish;

           Indicates that no more data will be fetched from this
           statement handle before it is either executed again or
           destroyed.  The `finish' method is rarely needed, but
           can sometimes be helpful in very specific situations
           to allow the server to free up resources (such as sort
           buffers).

           When all the data has been fetched from a `SELECT'
           statement, the driver should automatically call `fin­
           ish' for you. So you should not normally need to call
           it explicitly.

           Consider a query like:

             SELECT foo FROM table WHERE bar=? ORDER BY foo

           where you want to select just the first (smallest)
           "foo" value from a very large table. When executed,
           the database server will have to use temporary buffer
           space to store the sorted rows. If, after executing
           the handle and selecting one row, the handle won't be
           re-executed for some time and won't be destroyed, the
           `finish' method can be used to tell the server that
           the buffer space can be freed.

           Calling `finish' resets the the Active entry elsewhere
           in this document attribute for the statement.  It may
           also make some statement handle attributes (such as
           `NAME' and `TYPE') unavailable if they have not
           already been accessed (and thus cached).

           The `finish' method does not affect the transaction
           status of the database connection.  It has nothing to
           do with transactions. It's mostly an internal "house­
           keeping" method that is rarely needed. There's no need
           to call `finish' if you're about to destroy or re-exe­
           cute the statement handle.  See also the disconnect

           entry elsewhere in this document attribute.

           The `finish' method should have been called `can­
           cel_select'.

       `rows'
             $rv = $sth->rows;

           Returns the number of rows affected by the last row
           affecting command, or -1 if the number of rows is not
           known or not available.

           Generally, you can only rely on a row count after a
           non-`SELECT' `execute' (for some specific operations
           like `UPDATE' and `DELETE'), or after fetching all the
           rows of a `SELECT' statement.

           For `SELECT' statements, it is generally not possible
           to know how many rows will be returned except by
           fetching them all.  Some drivers will return the num­
           ber of rows the application has fetched so far, but
           others may return -1 until all rows have been fetched.
           So use of the `rows' method or `$DBI::rows' with
           `SELECT' statements is not recommended.

           One alternative method to get a row count for a
           `SELECT' is to execute a "SELECT COUNT(*) FROM ..."
           SQL statement with the same "..." as your query and
           then fetch the row count from that.

       `bind_col'
             $rc = $sth->bind_col($column_number, \$var_to_bind);

           Binds an output column (field) of a `SELECT' statement
           to a Perl variable.  See `bind_columns' below for an
           example.  Note that column numbers count up from 1.

           Whenever a row is fetched from the database, the cor­
           responding Perl variable is automatically updated.
           There is no need to fetch and assign the values manu­
           ally.  The binding is performed at a very low level
           using Perl aliasing so there is no extra copying tak­
           ing place.  This makes using bound variables very
           efficient.

           For maximum portability between drivers, `bind_col'
           should be called after `execute'. This restriction may
           be removed in a later version of the DBI.

           You do not need to bind output columns in order to
           fetch data, but it can be useful for some applications
           which need either maximum performance or greater clar­
           ity of code.  The the bind_param entry elsewhere in

           function for input variables.

       `bind_columns'
             $rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);

           Calls the bind_col entry elsewhere in this document
           for each column of the `SELECT' statement.  The
           `bind_columns' method will die if the number of refer­
           ences does not match the number of fields.

           For maximum portability between drivers,
           `bind_columns' should be called after `execute'.

           For example:

             $dbh->{RaiseError} = 1; # do this, or check every call for errors
             $sth = $dbh->prepare(q{ SELECT region, sales FROM sales_by_region });
             $sth->execute;
             my ($region, $sales);

             # Bind Perl variables to columns:
             $rv = $sth->bind_columns(\$region, \$sales);

             # you can also use Perl's \(...) syntax (see perlref docs):
             #     $sth->bind_columns(\($region, $sales));

             # Column binding is the most efficient way to fetch data
             while ($sth->fetch) {
                 print "$region: $sales\n";
             }

           For compatibility with old scripts, the first parame­
           ter will be ignored if it is `undef' or a hash refer­
           ence.

           Here's a more fancy example that binds columns to the
           values inside a hash (thanks to H.Merijn Brand):

             $sth->execute;
             my %row;
             $sth->bind_columns( \( @row{ @{$sth->{NAME_lc} } } ));
             while ($sth->fetch) {
                 print "$row{region}: $row{sales}\n";
             }

       `dump_results'
             $rows = $sth->dump_results($maxlen, $lsep, $fsep, $fh);

           Fetches all the rows from `$sth', calls
           `DBI::neat_list' for each row, and prints the results
           to `$fh' (defaults to `STDOUT') separated by `$lsep'
           (default `"\n"'). `$fsep' defaults to `", "' and


           This method is designed as a handy utility for proto­
           typing and testing queries. Since it uses the
           neat_list entry elsewhere in this document to format
           and edit the string for reading by humans, it is not
           recomended for data transfer applications.

       Statement Handle Attributes

       This section describes attributes specific to statement
       handles. Most of these attributes are read-only.

       Changes to these statement handle attributes do not affect
       any other existing or future statement handles.

       Attempting to set or get the value of an unknown attribute
       is fatal, except for private driver specific attributes
       (which all have names starting with a lowercase letter).

       Example:

         ... = $h->{NUM_OF_FIELDS};    # get/read

       Note that some drivers cannot provide valid values for
       some or all of these attributes until after `$sth-'>`exe­
       cute' has been called.

       See also the finish entry elsewhere in this document to
       learn more about the effect it may have on some
       attributes.

       `NUM_OF_FIELDS'  (integer, read-only)
           Number of fields (columns) the prepared statement will
           return. Non-`SELECT' statements will have
           `NUM_OF_FIELDS == 0'.

       `NUM_OF_PARAMS'  (integer, read-only)
           The number of parameters (placeholders) in the pre­
           pared statement.  See SUBSTITUTION VARIABLES below for
           more details.

       `NAME'  (array-ref, read-only)
           Returns a reference to an array of field names for
           each column. The names may contain spaces but should
           not be truncated or have any trailing space. Note that
           the names have the letter case (upper, lower or mixed)
           as returned by the driver being used. Portable appli­
           cations should use the NAME_lc entry elsewhere in this
           document or the NAME_uc entry elsewhere in this docu­
           ment.

             print "First column name: $sth->{NAME}->[0]\n";

           Like the NAME entry elsewhere in this document but
           always returns lowercase names.

       `NAME_uc'  (array-ref, read-only)
           Like the NAME entry elsewhere in this document but
           always returns uppercase names.

       `TYPE'  (array-ref, read-only)
           Returns a reference to an array of integer values for
           each column. The value indicates the data type of the
           corresponding column.

           The values correspond to the international standards
           (ANSI X3.135 and ISO/IEC 9075) which, in general
           terms, means ODBC. Driver-specific types that don't
           exactly match standard types should generally return
           the same values as an ODBC driver supplied by the mak­
           ers of the database. That might include private type
           numbers in ranges the vendor has officially registered
           with the ISO working group:

             ftp://jerry.ece.umassd.edu/isowg3/dbl/SQL_Registry

           Where there's no vendor-supplied ODBC driver to be
           compatible with, the DBI driver can use type numbers
           in the range that is now officially reserved for use
           by the DBI: -9999 to -9000.

           All possible values for `TYPE' should have at least
           one entry in the output of the `type_info_all' method
           (see the type_info_all entry elsewhere in this docu­
           ment).

       `PRECISION'  (array-ref, read-only)
           Returns a reference to an array of integer values for
           each column.  For non-numeric columns, the value gen­
           erally refers to either the maximum length or the
           defined length of the column.  For numeric columns,
           the value refers to the maximum number of significant
           digits used by the data type (without considering a
           sign character or decimal point).  Note that for
           floating point types (REAL, FLOAT, DOUBLE), the "dis­
           play size" can be up to 7 characters greater than the
           precision.  (for the sign + decimal point + the letter
           E + a sign + 2 or 3 digits).

       `SCALE'  (array-ref, read-only)
           Returns a reference to an array of integer values for
           each column.  NULL (`undef') values indicate columns
           where scale is not applicable.

       `NULLABLE'  (array-ref, read-only)
           Returns a reference to an array indicating the

           values are `0' (or an empty string) = no, `1' = yes,
           `2' = unknown.

             print "First column may return NULL\n" if $sth->{NULLABLE}->[0];

       `CursorName'  (string, read-only)
           Returns the name of the cursor associated with the
           statement handle, if available. If not available or if
           the database driver does not support the `"where cur­
           rent of ..."' SQL syntax, then it returns `undef'.

       `Statement'  (string, read-only)
           Returns the statement string passed to the the prepare
           entry elsewhere in this document method.

       `RowsInCache'  (integer, read-only)
           If the driver supports a local row cache for `SELECT'
           statements, then this attribute holds the number of
           un-fetched rows in the cache. If the driver doesn't,
           then it returns `undef'. Note that some drivers pre-
           fetch rows on execute, whereas others wait till the
           first fetch.

           See also the the RowCacheSize entry elsewhere in this
           document database handle attribute.


FURTHER INFORMATION

       Transactions

       Transactions are a fundamental part of any robust database
       system. They protect against errors and database corrup­
       tion by ensuring that sets of related changes to the
       database take place in atomic (indivisible, all-or-noth­
       ing) units.

       This section applies to databases that support transac­
       tions and where `AutoCommit' is off.  See the AutoCommit
       entry elsewhere in this document for details of using
       `AutoCommit' with various types of databases.

       The recommended way to implement robust transactions in
       Perl applications is to use `RaiseError' and
       `eval { ... }' (which is very fast, unlike `eval "..."').
       For example:

         $dbh->{RaiseError} = 1;
         eval {
             foo(...)        # do lots of work here
             bar(...)        # including inserts
             baz(...)        # and updates
             $dbh->commit;   # commit the changes if we get this far
         };
         if ($@) {
             warn "Transaction aborted because $@";
             $dbh->rollback; # undo the incomplete changes
             # add other application on-error-clean-up code here
         }

       If the `RaiseError' attribute is not set, then DBI calls
       would need to be manually checked for errors, typically
       like this:

         $h->method(@args) or die $h->errstr;

       With `RaiseError' set, the DBI will automatically `die' if
       any DBI method call on that handle (or a child handle)
       fails, so you don't have to test the return value of each
       method call. See the RaiseError entry elsewhere in this
       document for more details.

       A major advantage of the `eval' approach is that the
       transaction will be properly rolled back if any code (not
       just DBI calls) in the inner application dies for any rea­
       son. The major advantage of using the `$h-'>`{RaiseError}'
       attribute is that all DBI calls will be checked automati­
       cally. Both techniques are strongly recommended.

       After calling `commit' or `rollback' many drivers will not
       let you fetch from a previously active `SELECT' statement
       handle that's a child of the same database handle. A typi­
       cal way round this is to connect the the database twice
       and use one connection for `SELECT' statements.

       Handling BLOB / LONG / Memo Fields

       Many databases support "blob" (binary large objects),
       "long", or similar datatypes for holding very long strings
       or large amounts of binary data in a single field. Some
       databases support variable length long values over
       2,000,000,000 bytes in length.

       Since values of that size can't usually be held in memory,
       and because databases can't usually know in advance the
       length of the longest long that will be returned from a
       `SELECT' statement (unlike other data types), some special
       handling is required.

       In this situation, the value of the `$h-'>`{LongReadLen}'

       allocate when fetching such fields.  The `$h-'>`{LongTrun­
       cOk}' attribute is used to determine how to behave if a
       fetched value can't fit into the buffer.

       When trying to insert long or binary values, placeholders
       should be used since there are often limits on the maximum
       size of an `INSERT' statement and the the quote entry
       elsewhere in this document method generally can't cope
       with binary data.  See the Placeholders and Bind Values
       entry elsewhere in this document.

       Simple Examples

       Here's a complete example program to select and fetch some
       data:

         my $dbh = DBI->connect("dbi:DriverName:db_name", $user, $password)
             or die "Can't connect to $data_source: $DBI::errstr";

         my $sth = $dbh->prepare( q{
                 SELECT name, phone
                 FROM mytelbook
         }) or die "Can't prepare statement: $DBI::errstr";

         my $rc = $sth->execute
             or die "Can't execute statement: $DBI::errstr";

         print "Query will return $sth->{NUM_OF_FIELDS} fields.\n\n";
         print "Field names: @{ $sth->{NAME} }\n";

         while (($name, $phone) = $sth->fetchrow_array) {
             print "$name: $phone\n";
         }
         # check for problems which may have terminated the fetch early
         die $sth->errstr if $sth->err;

         $dbh->disconnect;

       Here's a complete example program to insert some data from
       a file.  (This example uses `RaiseError' to avoid needing
       to check each call).

         my $dbh = DBI->connect("dbi:DriverName:db_name", $user, $password, {
             RaiseError => 1, AutoCommit => 0
         });

         my $sth = $dbh->prepare( q{
             INSERT INTO table (name, phone) VALUES (?, ?)
         });

         while (<FH>) {
             chomp;
             my ($name, $phone) = split /,/;
             $sth->execute($name, $phone);
         }
         close FH;

         $dbh->commit;
         $dbh->disconnect;

       Here's how to convert fetched NULLs (undefined values)
       into empty strings:

         while($row = $sth->fetchrow_arrayref) {
           # this is a fast and simple way to deal with nulls:
           foreach (@$row) { $_ = '' unless defined }
           print "@$row\n";
         }

       The `q{...}' style quoting used in these examples avoids
       clashing with quotes that may be used in the SQL state­
       ment. Use the double-quote like `qq{...}' operator if you
       want to interpolate variables into the string.  See the
       Quote and Quote-like Operators entry in the perlop manpage
       for more details.

       Threads and Thread Safety

       Perl versions 5.004_50 and later include optional experi­
       mental support for multiple threads on many platforms.  If
       the DBI is built using a Perl that has threads enabled
       then it will use a per-driver mutex to ensure that only
       one thread is with a driver at any one time.  Please note
       that support for threads in Perl is still experimental and
       is known to have some significant problems. It's use is
       not recommended.

       Signal Handling and Canceling Operations

       The first thing to say is that signal handling in Perl is
       currently not safe. There is always a small risk of Perl
       crashing and/or core dumping when, or after, handling a
       signal.  (The risk was reduced with 5.004_04 but is still
       present.)

       The two most common uses of signals in relation to the DBI
       are for canceling operations when the user types Ctrl-C
       (interrupt), and for implementing a timeout using
       `alarm()' and `$SIG{ALRM}'.

       To assist in implementing these operations, the DBI pro­
       vides a `cancel' method for statement handles. The `can­
       cel' method should abort the current operation and is


       However, it must be stressed that: a) few drivers imple­
       ment this at the moment (the DBI provides a default method
       that just returns `undef'); and b) even if implemented,
       there is still a possibility that the statement handle,
       and possibly the parent database handle, will not be
       usable afterwards.

       If `cancel' returns true, then it has successfully invoked
       the database engine's own cancel function.  If it returns
       false, then `cancel' failed. If it returns `undef', then
       the database engine does not have cancel implemented.


DEBUGGING

       In addition to the the trace entry elsewhere in this docu­
       ment method, you can enable the same trace information by
       setting the `DBI_TRACE' environment variable before start­
       ing Perl.

       On Unix-like systems using a Bourne-like shell, you can do
       this easily on the command line:

         DBI_TRACE=2 perl your_test_script.pl

       If `DBI_TRACE' is set to a non-numeric value, then it is
       assumed to be a file name and the trace level will be set
       to 2 with all trace output appended to that file. If the
       name begins with a number followed by an equal sign (`='),
       then the number and the equal sign are stripped off from
       the name, and the number is used to set the trace level.
       For example:

         DBI_TRACE=1=dbitrace.log perl your_test_script.pl

       See also the the trace entry elsewhere in this document
       method.

       It can sometimes be handy to compare trace files from two
       different runs of the same script. However using a tool
       like `diff' doesn't work well because the trace file is
       full of object addresses that may differ each run. Here's
       a handy little command to strip those out:

        perl -pe 's/\b0x[\da-f]{6,}/0xNNNN/gi; s/\b[\da-f]{6,}/<long number>/gi'


WARNING AND ERROR MESSAGES

       Fatal Errors

       Can't call method ""prepare"" without a package or object
           refer­ ence
           The `$dbh' handle you're using to call `prepare' is

           failed. You should always check the return status of
           DBI methods, or use the the RaiseError entry elsewhere
           in this document attribute.

       Can't call method ""execute"" without a package or object
           refer­ ence
           The `$sth' handle you're using to call `execute' is
           probably undefined because the preceeding `prepare'
           failed. You should always check the return status of
           DBI methods, or use the the RaiseError entry elsewhere
           in this document attribute.

       DBI/DBD internal version mismatch
           The DBD driver module was built with a different ver­
           sion of DBI than the one currently being used.  You
           should rebuild the DBD module under the current ver­
           sion of DBI.

           (Some rare platforms require "static linking". On
           those platforms, there may be an old DBI or DBD driver
           version actually embedded in the Perl executable being
           used.)

       DBD driver has not implemented the AutoCommit attribute
           The DBD driver implementation is incomplete. Consult
           the author.

       Can't [sg]et %s->{%s}: unrecognised attribute
           You attempted to set or get an unknown attribute of a
           handle.  Make sure you have spelled the attribute name
           correctly; case is significant (e.g., "Autocommit" is
           not the same as "AutoCommit").

       Warnings

       Database handle destroyed without explicit disconnect
           A `$dbh' handle went out of scope or the program ended
           before the handle was disconnected from the database.
           You should always explicitly call `disconnect' when
           you are finished using a database handle. If using
           transactions then you should also explicitly call
           `commit' or `rollback' before `disconnect'.

       DBI Handle cleared whilst still holding %d cached kids!
           Most probably due to a DBI bug. Possibly a DBD driver
           bug. Please report it.

       DBI Handle cleared whilst still active!
           Most probably due to a DBI bug. Possibly a DBD driver
           bug. Please report it.

           Most probably a DBD driver bug. Please report it.

       DBI Handle has %d uncleared child handles
           Most probably due to a DBI bug. Possibly a DBD driver
           bug. Please report it.


SEE ALSO

       Driver and Database Documentation

       Refer to the documentation for the DBD driver that you are
       using.

       Refer to the SQL Language Reference Manual for the
       database engine that you are using.

       Books and Journals

        Programming the Perl DBI, by Alligator Descartes and Tim Bunce.

        Programming Perl 2nd Ed. by Larry Wall, Tom Christiansen & Randal Schwartz.

        Learning Perl by Randal Schwartz.

        Dr Dobb's Journal, November 1996.

        The Perl Journal, April 1997.

       Manual Pages

       perl(1), perlmod(1), perlbook(1)

       Mailing List

       The dbi-users mailing list is the primary means of commu­
       nication among users of the DBI and its related modules.
       For details send email to:

        dbi-users-help@perl.org

       There are typically between 700 and 900 messages per
       month.  You have to subscribe in order to be able to post.
       However you can opt for a 'post-only' subscription.

       Mailing list archives are held at:

        http://www.xray.mpe.mpg.de/mailing-lists/dbi/
        http://groups.yahoo.com/group/dbi-users
        http://www.bitmechanic.com/mail-archives/dbi-users/
        http://marc.theaimsgroup.com/?l=perl-dbi&r=1&w=2
        http://www.mail-archive.com/dbi-users%40perl.org/
        http://www.mail-archive.com/dbi-users%40perl.org/


       The DBI "Home Page":

        http://dbi.perl.org/

       Other DBI related links:

        http://tegan.deltanet.com/~phlip/DBUIdoc.html
        http://dc.pm.org/perl_db.html
        http://wdvl.com/Authoring/DB/Intro/toc.html
        http://www.hotwired.com/webmonkey/backend/tutorials/tutorial1.html
        http://bumppo.net/lists/macperl/1999/06/msg00197.html

       Other database related links:

        http://www.jcc.com/sql_stnd.html
        http://cuiwww.unige.ch/OSG/info/FreeDB/FreeDB.home.html

       Commercial and Data Warehouse Links

        http://www.dwinfocenter.org
        http://www.datawarehouse.com
        http://www.datamining.org
        http://www.olapcouncil.org
        http://www.idwa.org
        http://www.knowledgecenters.org/dwcenter.asp

       Recommended Perl Programming Links

        http://language.perl.com/style/

       FAQ

       Please also read the DBI FAQ which is installed as a
       DBI::FAQ module.  You can use perldoc to read it by exe­
       cuting the `perldoc DBI::FAQ' command.


AUTHORS

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


COPYRIGHT

       The DBI module is Copyright (c) 1994-2000 Tim Bunce. Eng­
       land.  All rights reserved.

       You may distribute under the terms of either the GNU Gen­
       eral Public License or the Artistic License, as specified
       in the Perl README file.


ACKNOWLEDGEMENTS

       I would like to acknowledge the valuable contributions of

       especially in the early years (1992-1994). In no particu­
       lar order: Kevin Stock, Buzz Moschetti, Kurt Andersen, Ted
       Lemon, William Hails, Garth Kennedy, Michael Peppler, Neil
       S. Briscoe, Jeff Urlwin, David J. Hughes, Jeff Stander,
       Forrest D Whitcher, Larry Wall, Jeff Fried, Roy Johnson,
       Paul Hudson, Georg Rehfeld, Steve Sizemore, Ron Pool, Jon
       Meek, Tom Christiansen, Steve Baumgarten, Randal Schwartz,
       and a whole lot more.

       Then, of course, there are the poor souls who have strug­
       gled through untold and undocumented obstacles to actually
       implement DBI drivers.  Among their ranks are Jochen Wied­
       mann, Alligator Descartes, Jonathan Leffler, Jeff Urlwin,
       Michael Peppler, Henrik Tougaard, Edwin Pratomo, Davide
       Migliavacca, Jan Pazdziora, Peter Haworth, Edmund Mergl,
       Steve Williams, Thomas Lowery, and Phlip Plumlee. Without
       them, the DBI would not be the practical reality it is
       today.  I'm also especially grateful to Alligator
       Descartes for starting work on the "Programming the Perl
       DBI" book and letting me jump on board.


TRANSLATIONS

       A German translation of this manual (possibly slightly out
       of date) is available, thanks to O'Reilly, at:

         http://www.oreilly.de/catalog/perldbiger/

       Some other translations:

        http://cronopio.net/perl/                              - Spanish
        http://member.nifty.ne.jp/hippo2000/dbimemo.htm        - Japanese


SUPPORT / WARRANTY

       The DBI is free software. IT COMES WITHOUT WARRANTY OF ANY
       KIND.

       Commercial support for Perl and the DBI, DBD::Oracle and
       Oraperl modules can be arranged via The Perl Clinic.  For
       more details visit:

         http://www.perlclinic.com


TRAINING

       References to DBI related training resources. No recommen­
       dation implied.

         http://www.treepax.co.uk/
         http://www.keller.com/dbweb/

       See the DBI FAQ for a more comprehensive list of FAQs. Use
       the `perldoc DBI::FAQ' command to read it.

       How fast is the DBI?

       To measure the speed of the DBI and DBD::Oracle code, I
       modified DBD::Oracle so you can set an attribute that will
       cause the same row to be fetched from the row cache over
       and over again (without involving Oracle code but exercis­
       ing *all* the DBI and DBD::Oracle code in the code path
       for a fetch).

       The results (on my lightly loaded old Sparc 10) fetching
       50000 rows using:

               1 while $csr->fetch;

       were:      one field:   5300 fetches per cpu second
       (approx)      ten fields:  4000 fetches per cpu second
       (approx)

       Obviously results will vary between platforms (newer
       faster platforms can reach around 50000 fetches per sec­
       ond), but it does give a feel for the maximum performance:
       fast.  By way of comparison, using the code:

               1 while @row = $csr->fetchrow_array;

       (`fetchrow_array' is roughly the same as `ora_fetch')
       gives:

               one field:   3100 fetches per cpu second (approx)
               ten fields:  1000 fetches per cpu second (approx)

       Notice the slowdown and the more dramatic impact of extra
       fields.  (The fields were all one char long. The impact
       would be even bigger for longer strings.)

       Changing that slightly to represent actually doing some­
       thing in Perl with the fetched data:

           while(@row = $csr->fetchrow_array) {
               $hash{++$i} = [ @row ];
           }

       gives:    ten fields:  500 fetches per cpu second (approx)

       That simple addition has *halved* the performance.

       I therefore conclude that DBI and DBD::Oracle overheads
       are small compared with Perl language overheads (and prob­
       ably database overheads).

       replacing your fetch loop with just:

               1 while $csr->fetch;

       and time that. If that helps then point the finger at your
       own code. If that doesn't help much then point the finger
       at the database, the platform, the network etc. But think
       carefully before pointing it at the DBI or your driver.

       (Having said all that, if anyone can show me how to make
       the DBI or drivers even more efficient, I'm all ears.)

       Why doesn't my CGI script work right?

       Read the information in the references below.  Please do
       not post CGI related questions to the dbi-users mailing
       list (or to me).

        http://www.perl.com/cgi-bin/pace/pub/doc/FAQs/cgi/perl-cgi-faq.html
        http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
        http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
        http://www.boutell.com/faq/
        http://www.perl.com/perl/faq/

       General problems and good ideas:

        Use the CGI::ErrorWrap module.
        Remember that many env vars won't be set for CGI scripts.

       How can I maintain a WWW connection to a database?

       For information on the Apache httpd server and the
       `mod_perl' module see

         http://perl.apache.org/

       What about ODBC?

       A DBD::ODBC module is available.

       Does the DBI have a year 2000 problem?

       No. The DBI has no knowledge or understanding of dates at
       all.

       Individual drivers (DBD::*) may have some date handling
       code but are unlikely to have year 2000 related problems
       within their code. However, your application code which
       uses the DBI and DBD drivers may have year 2000 related
       problems if it has not been designed and written well.

       of the Perl FAQ:

         http://www.perl.com/CPAN/doc/FAQs/FAQ/PerlFAQ.html


OTHER RELATED WORK AND PERL MODULES

       Apache::DBI by E.Mergl@bawue.de
           To be used with the Apache daemon together with an
           embedded Perl interpreter like `mod_perl'. Establishes
           a database connection which remains open for the life­
           time of the HTTP daemon. This way the CGI connect and
           disconnect for every database access becomes superflu­
           ous.

       JDBC Server by Stuart 'Zen' Bishop zen@bf.rmit.edu.au
           The server is written in Perl. The client classes that
           talk to it are of course in Java. Thus, a Java applet
           or application will be able to comunicate via the JDBC
           API with any database that has a DBI driver installed.
           The URL used is in the form
           `jdbc:dbi://host.domain.etc:999/Driver/DBName'.  It
           seems to be very similar to some commercial products,
           such as jdbcKona.

       Remote Proxy DBD support
           As of DBI 1.02, a complete implementation of a
           DBD::Proxy driver and the DBI::ProxyServer are part of
           the DBI distribution.

       SQL Parser
                   Hugo van der Sanden <hv@crypt.compulink.co.uk>
                   Stephen Zander <stephen.zander@mckesson.com>

           Based on the O'Reilly lex/yacc book examples and
           `byacc'.

           See also the SQL::Statement module, a very simple SQL
           parser and engine, base of the DBD::CSV driver.


Man(1) output converted with man2html