subselect_hash_sj_engine Class Reference

#include <item_subselect.h>

Inheritance diagram for subselect_hash_sj_engine:

List of all members.

Public Member Functions
	subselect_hash_sj_engine (THD *thd, Item_subselect *in_predicate, subselect_single_select_engine *old_engine)
bool	setup (List< Item > *tmp_columns)
virtual void	cleanup ()
virtual bool	prepare ()
virtual bool	exec ()
virtual void	print (String *str, enum_query_type query_type)
virtual uint	cols () const
virtual enum_engine_type	engine_type () const
const st_join_table *	get_join_tab () const
Item *	get_cond_for_explain () const

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Detailed Description

Compute an IN predicate via a hash semi-join. The subquery is materialized during the first evaluation of the IN predicate. The IN predicate is executed via the functionality inherited from subselect_indexsubquery_engine.

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Member Function Documentation

void subselect_hash_sj_engine::cleanup

(

)

[virtual]

Cleanup performed after each PS execution.

Called in the end of JOIN::prepare for PS from Item_subselect::cleanup.

Reimplemented from subselect_indexsubquery_engine.

bool subselect_hash_sj_engine::exec

(

)

[virtual]

Execute a subquery IN predicate via materialization.

If needed materialize the subquery into a temporary table, then copmpute the predicate via a lookup into this table.

Return values:

TRUE	if error
FALSE	otherwise

Reimplemented from subselect_indexsubquery_engine.

void subselect_hash_sj_engine::print	(	String *	str,
		enum_query_type	query_type
	)		[virtual]

Print the state of this engine into a string for debugging and views.

Reimplemented from subselect_indexsubquery_engine.

bool subselect_hash_sj_engine::setup

(

List< Item > *

tmp_columns

)

Create all structures needed for subquery execution using hash semijoin.

• Create a temporary table to store the result of the IN subquery. The temporary table has one hash index on all its columns. If single-column, the index allows at most one NULL row.
• Create a new result sink that sends the result stream of the subquery to the temporary table,
• Create and initialize a new JOIN_TAB, and TABLE_REF objects to perform lookups into the indexed temporary table.

Parameters:

tmp_columns

columns of temporary table

: Currently Item_subselect::init() already chooses and creates at parse time an engine with a corresponding JOIN to execute the subquery.

Return values:

TRUE	if error
FALSE	otherwise

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The documentation for this class was generated from the following files:

• item_subselect.h
• item_subselect.cc