# DBI::DBD::SqlEngine - phpMan

## NAME
    [DBI::DBD::SqlEngine] - Base class for DBI drivers without their own SQL
    engine

## SYNOPSIS
        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 { ... }

## DESCRIPTION
    [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].

    [DBI::DBD::SqlEngine] 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], 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]:
   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]
    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] 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] (readonly)

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

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

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

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

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

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

   sql_identifier_case
    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

      SELECT * FROM foo

   sql_quoted_identifier_case
    Contains how [DBI::DBD::SqlEngine] 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]. Because an
    [SQL::Parser] 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]. 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 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]. 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] 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].

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

    See "[DBI::DBD::SqlEngine::TableSource]" for details.

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

    See "[DBI::DBD::SqlEngine::DataSource]" 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] 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] 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";
        __END__
        # [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).

   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]
    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.

   [DBI::DBD::SqlEngine::DataSource]
    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].

## SQL ENGINES
    [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.

## SUPPORT
    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

        <<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], [DBD::DBM] and [DBD::AnyData]. 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], [DBD::AnyData] and [DBD::Sys].