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subselect_single_select_engine Class Reference
Inheritance diagram for subselect_single_select_engine:
subselect_engine Sql_alloc

List of all members.

Public Member Functions

 subselect_single_select_engine (st_select_lex *select, select_result_interceptor *result, Item_subselect *item)
virtual void cleanup ()
virtual bool prepare ()
virtual void fix_length_and_dec (Item_cache **row)
virtual bool exec ()
virtual uint cols () const
virtual uint8 uncacheable () const
virtual void exclude ()
virtual table_map upper_select_const_tables () const
virtual void print (String *str, enum_query_type query_type)
virtual bool change_result (Item_subselect *si, select_result_interceptor *result)
virtual bool no_tables () const
virtual bool may_be_null () const
virtual bool is_executed () const
virtual enum_engine_type engine_type () const


class subselect_hash_sj_engine
class Item_in_subselect

Member Function Documentation

bool subselect_single_select_engine::change_result ( Item_subselect si,
select_result_interceptor *  res 
) [virtual]

change select_result object of engine.

sinew subselect Item
resnew select_result object
Return values:

Implements subselect_engine.

Cleanup engine after complete query execution, free all resources.

Implements subselect_engine.

Report about presence of tables in subquery.

Return values:
TRUEthere are not tables used in subquery
FALSEthere are some tables in subquery

Implements subselect_engine.

Create and prepare the JOIN object that represents the query execution plan for the subquery.

This method is called from Item_subselect::fix_fields. For prepared statements it is called both during the PREPARE and EXECUTE phases in the following ways:

  • During PREPARE the optimizer needs some properties (join->fields_list.elements) of the JOIN to proceed with preparation of the remaining query (namely to complete ::fix_fields for the subselect related classes. In the end of PREPARE the JOIN is deleted.
  • When we EXECUTE the query, Item_subselect::fix_fields is called again, and the JOIN object is re-created again, prepared and executed. In the end of execution it is deleted. In all cases the JOIN is created in runtime memory (not in the permanent memory root).
Re-check what properties of 'join' are needed during prepare, and see if we can avoid creating a JOIN during JOIN::prepare of the outer join.
Return values:
0if success
1if error

Implements subselect_engine.

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