Section: User Contributed Perl Documentation (3pm)
Updated: 2013-06-24
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DBI::DBD::SqlEngine - Base class for DBI drivers without their own SQL engine  


    package DBD::myDriver;

    use base qw(DBI::DBD::SqlEngine);

    sub driver
        my $drh = $proto->SUPER::driver($attr);
        return $drh->{class};

    package DBD::myDriver::dr;

    @ISA = qw(DBI::DBD::SqlEngine::dr);

    sub data_sources { ... }

    package DBD::myDriver::db;

    @ISA = qw(DBI::DBD::SqlEngine::db);

    sub init_valid_attributes { ... }
    sub init_default_attributes { ... }
    sub set_versions { ... }
    sub validate_STORE_attr { my ($dbh, $attrib, $value) = @_; ... }
    sub validate_FETCH_attr { my ($dbh, $attrib) = @_; ... }
    sub get_myd_versions { ... }
    sub get_avail_tables { ... }

    package DBD::myDriver::st;

    @ISA = qw(DBI::DBD::SqlEngine::st);

    sub FETCH { ... }
    sub STORE { ... }

    package DBD::myDriver::Statement;

    @ISA = qw(DBI::DBD::SqlEngine::Statement);

    sub open_table { ... }

    package DBD::myDriver::Table;

    @ISA = qw(DBI::DBD::SqlEngine::Table);

    sub new { ... }



DBI::DBD::SqlEngine abstracts the usage of SQL engines from the DBD. DBD authors can concentrate on the data retrieval they want to provide.

It is strongly recommended that you read DBD::File::Developers and DBD::File::Roadmap, because many of the DBD::File API is provided by DBI::DBD::SqlEngine.

Currently the API of DBI::DBD::SqlEngine is experimental and will likely change in the near future to provide the table meta data basics like DBD::File.  


The following attributes are handled by DBI itself and not by DBI::DBD::SqlEngine, thus they all work as expected:

    CompatMode             (Not used)
    Warn                   (Not used)

The following DBI attributes are handled by DBI::DBD::SqlEngine:


Always on.




Valid after "$sth->execute".


Valid after "$sth->prepare".


Valid after "$sth->execute"; probably undef for Non-Select statements.


Not really working, always returns an array ref of ones, as DBD::CSV does not verify input data. Valid after "$sth->execute"; undef for non-select statements.

The following DBI attributes and methods are not supported:


DBI::DBD::SqlEngine specific attributes

In addition to the DBI attributes, you can use the following dbh attributes:


Contains the module version of this driver (readonly)


Contains the module version of DBI::SQL::Nano (readonly)


Contains the module version of SQL::Statement, if available (readonly)


Contains the SQL Statement engine, either DBI::SQL::Nano or SQL::Statement (readonly).


Contains an instantiated instance of SQL::Parser (readonly). This is filled when used first time (only when used with SQL::Statement).


Contains an internally used DBD::Sponge handle (readonly).


Contains the list of valid attributes for each DBI::DBD::SqlEngine based driver (readonly).


Contains the list of those attributes which are readonly (readonly).


Contains how DBI::DBD::SqlEngine deals with non-quoted SQL identifiers:

  * SQL_IC_UPPER (1) means all identifiers are internally converted
    into upper-cased pendants
  * SQL_IC_LOWER (2) means all identifiers are internally converted
    into lower-cased pendants
  * SQL_IC_MIXED (4) means all identifiers are taken as they are

These conversions happen if (and only if) no existing identifier matches. Once existing identifier is used as known.

The SQL statement execution classes doesn't have to care, so don't expect "sql_identifier_case" affects column names in statements like



Contains how DBI::DBD::SqlEngine deals with quoted SQL identifiers (readonly). It's fixated to SQL_IC_SENSITIVE \fIs0(3), which is interpreted as SQL_IC_MIXED.


Contains additional flags to instantiate an SQL::Parser. Because an SQL::Parser is instantiated only once, it's recommended to set this flag before any statement is executed.


Controls the dialect understood by SQL::Parser. Possible values (delivery state of SQL::Statement):

  * ANSI
  * CSV
  * AnyData

Defaults to ``CSV''. Because an SQL::Parser is instantiated only once and SQL::Parser doesn't allow to modify the dialect once instantiated, it's strongly recommended to set this flag before any statement is executed (best place is connect attribute hash).


This value has a true value in case of this driver is operated via DBD::Gofer. The impact of being operated via Gofer is a read-only driver (not read-only databases!), so you cannot modify any attributes later - neither any table settings. But you won't get an error in cases you modify table attributes, so please carefully watch "sql_engine_in_gofer".


Private data area which contains information about the tables this module handles. Table meta data might not be available until the table has been accessed for the first time e.g., by issuing a select on it however it is possible to pre-initialize attributes for each table you use.

DBI::DBD::SqlEngine recognizes the (public) attributes "col_names", "table_name", "readonly", "sql_data_source" and "sql_identifier_case". Be very careful when modifying attributes you do not know, the consequence might be a destroyed or corrupted table.

While "sql_meta" is a private and readonly attribute (which means, you cannot modify it's values), derived drivers might provide restricted write access through another attribute. Well known accessors are "csv_tables" for DBD::CSV, "ad_tables" for DBD::AnyData and "dbm_tables" for DBD::DBM.


Controls the class which will be used for fetching available tables.

See ``DBI::DBD::SqlEngine::TableSource'' for details.


Contains the class name to be used for opening tables.

See ``DBI::DBD::SqlEngine::DataSource'' for details.  

Driver private methods

Default DBI methods


The "data_sources" method returns a list of subdirectories of the current directory in the form ``dbi:CSV:f_dir=$dirname''.

If you want to read the subdirectories of another directory, use

    my ($drh)  = DBI->install_driver ("CSV");
    my (@list) = $drh->data_sources (f_dir => "/usr/local/csv_data");


This method returns a list of file names inside $dbh->{f_dir}. Example:

    my ($dbh)  = DBI->connect ("dbi:CSV:f_dir=/usr/local/csv_data");
    my (@list) = $dbh->func ("list_tables");

Note that the list includes all files contained in the directory, even those that have non-valid table names, from the view of SQL.

Additional methods

The following methods are only available via their documented name when DBI::DBD::SQlEngine is used directly. Because this is only reasonable for testing purposes, the real names must be used instead. Those names can be computed by replacing the "sql_" in the method name with the driver prefix.



  sub sql_versions (;$) {
    my ($table_name) = @_;
    $table_name ||= ".";

Returns the versions of the driver, including the DBI version, the Perl version, DBI::PurePerl version (if DBI::PurePerl is active) and the version of the SQL engine in use.

    my $dbh = DBI->connect ("dbi:File:");
    my $sql_versions = $dbh->func( "sql_versions" );
    print "$sql_versions\n";
    # DBI::DBD::SqlEngine  0.05 using SQL::Statement 1.402
    # DBI                  1.623
    # OS                   netbsd (6.99.12)
    # Perl                 5.016002 (x86_64-netbsd-thread-multi)

Called in list context, sql_versions will return an array containing each line as single entry.

Some drivers might use the optional (table name) argument and modify version information related to the table (e.g. DBD::DBM provides storage backend information for the requested table, when it has a table name).



    sub sql_get_meta ($$)
        my ($table_name, $attrib) = @_;

Returns the value of a meta attribute set for a specific table, if any. See sql_meta for the possible attributes.

A table name of "." (single dot) is interpreted as the default table. This will retrieve the appropriate attribute globally from the dbh. This has the same restrictions as "$dbh->{$attrib}".



    sub sql_set_meta ($$$)
        my ($table_name, $attrib, $value) = @_;

Sets the value of a meta attribute set for a specific table. See sql_meta for the possible attributes.

A table name of "." (single dot) is interpreted as the default table which will set the specified attribute globally for the dbh. This has the same restrictions as "$dbh->{$attrib} = $value".



    sub sql_clear_meta ($)
        my ($table_name) = @_;

Clears the table specific meta information in the private storage of the dbh.  



Provides data sources and table information on database driver and database handle level.

  package DBI::DBD::SqlEngine::TableSource;

  sub data_sources ($;$)
    my ( $class, $drh, $attrs ) = @_;

  sub avail_tables
    my ( $class, $drh ) = @_;

The "data_sources" method is called when the user invokes any of the following:

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

The "avail_tables" method is called when the user invokes any of the following:

  @names = $dbh->tables( $catalog, $schema, $table, $type );
  $sth = $dbh->table_info( $catalog, $schema, $table, $type );
  $sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );

  $dbh->func( "list_tables" );

Every time where an "\%attr" argument can be specified, this "\%attr" object's "sql_table_source" attribute is preferred over the $dbh attribute or the driver default, eg.

  @ary = DBI->data_sources("dbi:CSV:", {
    f_dir => "/your/csv/tables",
    # note: this class doesn't comes with DBI
    sql_table_source => "DBD::File::Archive::Tar::TableSource",
    # scan tarballs instead of directories

When you're going to implement such a DBD::File::Archive::Tar::TableSource class, remember to add correct attributes (including "sql_table_source" and "sql_data_source") to the returned DSN's.


Provides base functionality for dealing with tables. It is primarily designed for allowing transparent access to files on disk or already opened (file-)streams (eg. for DBD::CSV).

Derived classes shall be restricted to similar functionality, too (eg. opening streams from an archive, transparently compress/uncompress log files before parsing them,

  package DBI::DBD::SqlEngine::DataSource;

  sub complete_table_name ($$;$)
    my ( $self, $meta, $table, $respect_case ) = @_;

The method "complete_table_name" is called when first setting up the meta information for a table:

  "SELECT user.id, user.name, user.shell FROM user WHERE ..."

results in opening the table "user". First step of the table open process is completing the name. Let's imagine you're having a DBD::CSV handle with following settings:

  $dbh->{sql_identifier_case} = SQL_IC_LOWER;
  $dbh->{f_ext} = '.lst';
  $dbh->{f_dir} = '/data/web/adrmgr';

Those settings will result in looking for files matching "[Uu][Ss][Ee][Rr](\.lst)?$" in "/data/web/adrmgr/". The scanning of the directory "/data/web/adrmgr/" and the pattern match check will be done in "DBD::File::DataSource::File" by the "complete_table_name" method.

If you intend to provide other sources of data streams than files, in addition to provide an appropriate "complete_table_name" method, a method to open the resource is required:

  package DBI::DBD::SqlEngine::DataSource;

  sub open_data ($)
    my ( $self, $meta, $attrs, $flags ) = @_;

After the method "open_data" has been run successfully, the table's meta information are in a state which allowes the table's data accessor methods will be able to fetch/store row information. Implementation details heavily depends on the table implementation, whereby the most famous is surely DBD::File::Table.  


DBI::DBD::SqlEngine currently supports two SQL engines: SQL::Statement and DBI::SQL::Nano::Statement_. DBI::SQL::Nano supports a very limited subset of SQL statements, but it might be faster for some very simple tasks. SQL::Statement in contrast supports a much larger subset of ANSI SQL.

To use SQL::Statement, you need at least version 1.401 of SQL::Statement and the environment variable "DBI_SQL_NANO" must not be set to a true value.  


You can find documentation for this module with the perldoc command.

    perldoc DBI::DBD::SqlEngine

You can also look for information at:

RT: CPAN's request tracker

<http://rt.cpan.org/NoAuth/Bugs.html?Dist=DBI> <http://rt.cpan.org/NoAuth/Bugs.html?Dist=SQL-Statement>

AnnoCPAN: Annotated CPAN documentation

<http://annocpan.org/dist/DBI> <http://annocpan.org/dist/SQL-Statement>

CPAN Ratings


Search CPAN



Where can I go for more help?

For questions about installation or usage, please ask on the dbi-dev@perl.org mailing list.

If you have a bug report, patch or suggestion, please open a new report ticket on CPAN, if there is not already one for the issue you want to report. Of course, you can mail any of the module maintainers, but it is less likely to be missed if it is reported on RT.

Report tickets should contain a detailed description of the bug or enhancement request you want to report and at least an easy way to verify/reproduce the issue and any supplied fix. Patches are always welcome, too.  


Thanks to Tim Bunce, Martin Evans and H.Merijn Brand for their continued support while developing DBD::File, DBD::DBM and DBD::AnyData. Their support, hints and feedback helped to design and implement this module.  


This module is currently maintained by

H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at googlemail.com >

The original authors are Jochen Wiedmann and Jeff Zucker.  


 Copyright (C) 2009-2013 by H.Merijn Brand & Jens Rehsack
 Copyright (C) 2004-2009 by Jeff Zucker
 Copyright (C) 1998-2004 by Jochen Wiedmann

All rights reserved.

You may freely distribute and/or modify this module under the terms of either the GNU General Public License (GPL) or the Artistic License, as specified in the Perl README file.  


DBI, DBD::File, DBD::AnyData and DBD::Sys.



Driver private methods
Where can I go for more help?