# man > DBI::DBD::SqlEngine(3pm)

## NAME
    [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) - Base class for DBI drivers without their own SQL engine

## SYNOPSIS
        package [DBD::myDriver](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AmyDriver/markdown);

        use base qw([DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown));

        sub driver
        {
            ...
            my $drh = $proto->[SUPER::driver](https://www.chedong.com/phpMan.php/perldoc/SUPER%3A%3Adriver/markdown)($attr);
            ...
            return $drh->{class};
            }

        package [DBD::myDriver::dr](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AmyDriver%3A%3Adr/markdown);

        @ISA = qw([DBI::DBD::SqlEngine::dr](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3Adr/markdown));

        sub data_sources { ... }
        ...

        package [DBD::myDriver::db](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AmyDriver%3A%3Adb/markdown);

        @ISA = qw([DBI::DBD::SqlEngine::db](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3Adb/markdown));

        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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AmyDriver%3A%3Ast/markdown);

        @ISA = qw([DBI::DBD::SqlEngine::st](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3Ast/markdown));

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

        package [DBD::myDriver::Statement](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AmyDriver%3A%3AStatement/markdown);

        @ISA = qw([DBI::DBD::SqlEngine::Statement](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3AStatement/markdown));

        sub open_table { ... }

        package [DBD::myDriver::Table](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AmyDriver%3A%3ATable/markdown);

        @ISA = qw([DBI::DBD::SqlEngine::Table](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ATable/markdown));

        sub new { ... }

## DESCRIPTION
    [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ADevelopers/markdown) and [DBD::File::Roadmap](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ARoadmap/markdown), because
    many of the [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown) API is provided by [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown).

    Currently the API of [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) is experimental and will likely change in the near
    future to provide the table meta data basics like [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown).

    [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) expects that any driver in inheritance chain has a DBI prefix.

### Metadata
    The following attributes are handled by DBI itself and not by [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown), thus they all
    work as expected:

        Active
        ActiveKids
        CachedKids
        CompatMode             (Not used)
        InactiveDestroy
        AutoInactiveDestroy
        Kids
        PrintError
        RaiseError
        Warn                   (Not used)

   The following DBI attributes are handled by [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown):
   AutoCommit
    Always on.

   ChopBlanks
    Works.

   NUM_OF_FIELDS
    Valid after "$sth->execute".

   NUM_OF_PARAMS
    Valid after "$sth->prepare".

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

   NULLABLE
    Not really working, always returns an array ref of ones, as [DBD::CSV](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ACSV/markdown) does not verify input data.
    Valid after "$sth->execute"; undef for non-select statements.

   The following DBI attributes and methods are not supported:
    bind_param_inout
    CursorName
    LongReadLen
    LongTruncOk

   [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) specific attributes
    In addition to the DBI attributes, you can use the following dbh attributes:

   sql_engine_version
    Contains the module version of this driver (readonly)

   sql_nano_version
    Contains the module version of [DBI::SQL::Nano](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ASQL%3A%3ANano/markdown) (readonly)

   sql_statement_version
    Contains the module version of [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown), if available (readonly)

   sql_handler
    Contains the SQL Statement engine, either [DBI::SQL::Nano](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ASQL%3A%3ANano/markdown) or [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown) (readonly).

   sql_parser_object
    Contains an instantiated instance of [SQL::Parser](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AParser/markdown) (readonly). This is filled when used first time
    (only when used with [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown)).

   sql_sponge_driver
    Contains an internally used [DBD::Sponge](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ASponge/markdown) handle (readonly).

   sql_valid_attrs
    Contains the list of valid attributes for each [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) based driver (readonly).

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

   sql_identifier_case
    Contains how [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) 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

      SELECT * FROM foo

   sql_quoted_identifier_case
    Contains how [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) deals with quoted SQL identifiers (readonly). It's fixated to
    SQL_IC_SENSITIVE (3), which is interpreted as SQL_IC_MIXED.

   sql_flags
    Contains additional flags to instantiate an [SQL::Parser](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AParser/markdown). Because an [SQL::Parser](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AParser/markdown) is instantiated
    only once, it's recommended to set this flag before any statement is executed.

   sql_dialect
    Controls the dialect understood by [SQL::Parser](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AParser/markdown). Possible values (delivery state of
    [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown)):

      * ANSI
      * CSV
      * AnyData

    Defaults to "CSV". Because an [SQL::Parser](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AParser/markdown) is instantiated only once and [SQL::Parser](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AParser/markdown) doesn't
    allow one 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).

   sql_engine_in_gofer
    This value has a true value in case of this driver is operated via [DBD::Gofer](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AGofer/markdown). 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".

   sql_meta
    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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ACSV/markdown), "ad_tables" for [DBD::AnyData](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AAnyData/markdown) and "dbm_tables" for
    [DBD::DBM](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ADBM/markdown).

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

    See "[DBI::DBD::SqlEngine::TableSource](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ATableSource/markdown)" for details.

   sql_data_source
    Contains the class name to be used for opening tables.

    See "[DBI::DBD::SqlEngine::DataSource](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ADataSource/markdown)" for details.

### Driver private methods
   Default DBI methods
   data_sources
    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");

   list_tables
    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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASQlEngine/markdown) 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.

   sql_versions
    Signature:

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

    Returns the versions of the driver, including the DBI version, the Perl version, [DBI::PurePerl](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3APurePerl/markdown)
    version (if [DBI::PurePerl](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3APurePerl/markdown) 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";
        __END__
        # [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown)  0.05 using [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ADBM/markdown) provides storage backend information for the requested table, when
    it has a table name).

   sql_get_meta
    Signature:

        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}".

   sql_set_meta
    Signature:

        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".

   sql_clear_meta
    Signature:

        sub sql_clear_meta ($)
        {
            my ($table_name) = @_;
            ...
        }

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

### Extensibility
   [DBI::DBD::SqlEngine::TableSource](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ATableSource/markdown)
    Provides data sources and table information on database driver and database handle level.

      package [DBI::DBD::SqlEngine::TableSource](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ATableSource/markdown);

      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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3AArchive%3A%3ATar%3A%3ATableSource/markdown)",
        # scan tarballs instead of directories
      });

    When you're going to implement such a [DBD::File::Archive::Tar::TableSource](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3AArchive%3A%3ATar%3A%3ATableSource/markdown) class, remember to
    add correct attributes (including "sql_table_source" and "sql_data_source") to the returned
    DSN's.

   [DBI::DBD::SqlEngine::DataSource](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ADataSource/markdown)
    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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ACSV/markdown)).

    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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ADataSource/markdown);

      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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ACSV/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ADataSource%3A%3AFile/markdown)" 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](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine%3A%3ADataSource/markdown);

      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](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile%3A%3ATable/markdown).

## SQL ENGINES
    [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown) currently supports two SQL engines: [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown) and
    [DBI::SQL::Nano::Statement_](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ASQL%3A%3ANano%3A%3AStatement/markdown). [DBI::SQL::Nano](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ASQL%3A%3ANano/markdown) supports a *very* limited subset of SQL statements,
    but it might be faster for some very simple tasks. [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown) in contrast supports a much
    larger subset of ANSI SQL.

    To use [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown), you need at least version 1.401 of [SQL::Statement](https://www.chedong.com/phpMan.php/perldoc/SQL%3A%3AStatement/markdown) and the environment
    variable "DBI_SQL_NANO" must not be set to a true value.

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

        perldoc [DBI::DBD::SqlEngine](https://www.chedong.com/phpMan.php/perldoc/DBI%3A%3ADBD%3A%3ASqlEngine/markdown)

    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

        <<http://cpanratings.perl.org/d/DBI>>

    *   Search CPAN

        <<http://search.cpan.org/dist/DBI/>>

  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.

## ACKNOWLEDGEMENTS
    Thanks to Tim Bunce, Martin Evans and H.Merijn Brand for their continued support while
    developing [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown), [DBD::DBM](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ADBM/markdown) and [DBD::AnyData](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AAnyData/markdown). Their support, hints and feedback helped to
    design and implement this module.

## AUTHOR
    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 AND LICENSE
     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.

## SEE ALSO
    DBI, [DBD::File](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AFile/markdown), [DBD::AnyData](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3AAnyData/markdown) and [DBD::Sys](https://www.chedong.com/phpMan.php/perldoc/DBD%3A%3ASys/markdown).