DBIx::Class::SQLMaker::LimitDialects(3pm)		User Contributed Perl Documentation		 DBIx::Class::SQLMaker::LimitDialects(3pm)

NAME

       DBIx::Class::SQLMaker::LimitDialects - SQL::Abstract::Limit-like functionality for DBIx::Class::SQLMaker

DESCRIPTION

       This module replicates a lot of the functionality originally found in SQL::Abstract::Limit. While simple limits would work as-is, the more
       complex dialects that require e.g. subqueries could not be reliably implemented without taking full advantage of the metadata locked within
       DBIx::Class::ResultSource classes. After reimplementation of close to 80% of the SQL::Abstract::Limit functionality it was deemed more
       practical to simply make an independent DBIx::Class-specific limit-dialect provider.

SQL LIMIT DIALECTS

       Note that the actual implementations listed below never use "*" literally.  Instead proper re-aliasing of selectors and order criteria is
       done, so that the limit dialect are safe to use on joined resultsets with clashing column names.

       Currently the provided dialects are:

   LimitOffset
	SELECT ... LIMIT $limit OFFSET $offset

       Supported by PostgreSQL and SQLite

   LimitXY
	SELECT ... LIMIT $offset $limit

       Supported by MySQL and any SQL::Statement based DBD

   RowNumberOver
	SELECT * FROM (
	 SELECT *, ROW_NUMBER() OVER( ORDER BY ... ) AS RNO__ROW__INDEX FROM (
	  SELECT ...
	 )
	) WHERE RNO__ROW__INDEX BETWEEN ($offset+1) AND ($limit+$offset)

       ANSI standard Limit/Offset implementation. Supported by DB2 and MSSQL >= 2005.

   SkipFirst
	SELECT SKIP $offset FIRST $limit * FROM ...

       Suported by Informix, almost like LimitOffset. According to SQL::Abstract::Limit "... SKIP $offset LIMIT $limit ..." is also supported.

   FirstSkip
	SELECT FIRST $limit SKIP $offset * FROM ...

       Supported by Firebird/Interbase, reverse of SkipFirst. According to SQL::Abstract::Limit "... ROWS $limit TO $offset ..." is also
       supported.

   RowNum
       Depending on the resultset attributes one of:

	SELECT * FROM (
	 SELECT *, ROWNUM rownum__index FROM (
	  SELECT ...
	 ) WHERE ROWNUM <= ($limit+$offset)
	) WHERE rownum__index >= ($offset+1)

       or

	SELECT * FROM (
	 SELECT *, ROWNUM rownum__index FROM (
	   SELECT ...
	 )
	) WHERE rownum__index BETWEEN ($offset+1) AND ($limit+$offset)

       or

	SELECT * FROM (
	   SELECT ...
	 ) WHERE ROWNUM <= ($limit+1)

       Supported by Oracle.

   Top
	SELECT * FROM

	SELECT TOP $limit FROM (
	 SELECT TOP $limit FROM (
	  SELECT TOP ($limit+$offset) ...
	 ) ORDER BY $reversed_original_order
	) ORDER BY $original_order

       Unreliable Top-based implementation, supported by MSSQL < 2005.

       CAVEAT

       Due to its implementation, this limit dialect returns incorrect results when $limit+$offset > total amount of rows in the resultset.

   FetchFirst
	SELECT * FROM
	(
	SELECT * FROM (
	 SELECT * FROM (
	  SELECT * FROM ...
	 ) ORDER BY $reversed_original_order
	   FETCH FIRST $limit ROWS ONLY
	) ORDER BY $original_order
	  FETCH FIRST $limit ROWS ONLY
	)

       Unreliable FetchFirst-based implementation, supported by IBM DB2 <= V5R3.

       CAVEAT

       Due to its implementation, this limit dialect returns incorrect results when $limit+$offset > total amount of rows in the resultset.

   RowCountOrGenericSubQ
       This is not exactly a limit dialect, but more of a proxy for Sybase ASE.  If no $offset is supplied the limit is simply performed as:

	SET ROWCOUNT $limit
	SELECT ...
	SET ROWCOUNT 0

       Otherwise we fall back to "GenericSubQ"

   GenericSubQ
	SELECT * FROM (
	 SELECT ...
	)
	WHERE (
	 SELECT COUNT(*) FROM $original_table cnt WHERE cnt.id < $original_table.id
	) BETWEEN $offset AND ($offset+$rows-1)

       This is the most evil limit "dialect" (more of a hack) for really stupid databases. It works by ordering the set by some unique column, and
       calculating the amount of rows that have a less-er value (thus emulating a "RowNum"-like index). Of course this implies the set can only be
       ordered by a single unique column. Also note that this technique can be and often is excruciatingly slow.

       Currently used by Sybase ASE, due to lack of any other option.

AUTHORS

       See "CONTRIBUTORS" in DBIx::Class.

LICENSE

       You may distribute this code under the same terms as Perl itself.

perl v5.14.2							    2011-08-19				 DBIx::Class::SQLMaker::LimitDialects(3pm)