item_subselect.h File Reference

#include <assert.h>
#include <sys/types.h>
#include <cstddef>
#include <memory>
#include <vector>
#include "field_types.h"
#include "my_alloc.h"
#include "my_inttypes.h"
#include "my_table_map.h"
#include "my_time.h"
#include "mysql/udf_registration_types.h"
#include "mysql_time.h"
#include "sql/comp_creator.h"
#include "sql/enum_query_type.h"
#include "sql/item.h"
#include "sql/iterators/row_iterator.h"
#include "sql/parse_location.h"
#include "sql/parse_tree_node_base.h"
#include "sql/sql_const.h"
#include "sql/sql_opt_exec_shared.h"
#include "template_utils.h"

Go to the source code of this file.

Classes
class	Item_subselect
struct	Item_subselect::Collect_subq_info
	argument used by walk method collect_scalar_subqueries ("css") More...
class	Item_singlerow_subselect
struct	Item_singlerow_subselect::Scalar_subquery_replacement
	Argument for walk method replace_scalar_subquery. More...
class	Item_maxmin_subselect
class	Item_exists_subselect
class	Item_in_subselect
	Representation of IN subquery predicates of the form "left_expr IN (SELECT ...)". More...
struct	Item_in_subselect::In2exists_info
	This bundles several pieces of information useful when doing the IN->EXISTS transform. More...
class	Item_allany_subselect
	ALL/ANY/SOME subselect. More...
class	SubqueryWithResult
class	subselect_indexsubquery_engine
	A subquery execution engine that evaluates the subquery by doing index lookups in a single table's index. More...
class	subselect_hash_sj_engine
	Compute an IN predicate via a hash semi-join. More...

Enumerations
enum class	Subquery_strategy : int {   UNSPECIFIED , CANDIDATE_FOR_IN2EXISTS_OR_MAT , CANDIDATE_FOR_SEMIJOIN , CANDIDATE_FOR_DERIVED_TABLE ,   SEMIJOIN , DERIVED_TABLE , SUBQ_EXISTS , SUBQ_MATERIALIZATION ,   DELETED }
	Strategy which will be used to handle this subquery: flattening to a semi-join, conversion to a derived table, rewrite of IN to EXISTS... Sometimes the strategy is first only a candidate, then the real decision happens in a second phase. More...

Functions
Item *	all_any_subquery_creator (Item *left_expr, chooser_compare_func_creator cmp, bool all, Query_block *select)
	Construct ALL/ANY/SOME subquery Item. More...
Item *	remove_in2exists_conds (Item *conds)
	Removes every predicate injected by IN->EXISTS. More...
bool	IsItemInSubSelect (Item *item)
	Returns whether the Item is an IN-subselect. More...

Enumeration Type Documentation

Subquery_strategy

enum class Subquery_strategy : int

strong

Strategy which will be used to handle this subquery: flattening to a semi-join, conversion to a derived table, rewrite of IN to EXISTS... Sometimes the strategy is first only a candidate, then the real decision happens in a second phase.

Other times the first decision is final.

Enumerator
UNSPECIFIED	Nothing decided yet.
CANDIDATE_FOR_IN2EXISTS_OR_MAT	Candidate for rewriting IN(subquery) to EXISTS, or subquery materialization.
CANDIDATE_FOR_SEMIJOIN	Candidate for semi-join flattening.
CANDIDATE_FOR_DERIVED_TABLE	Candidate for rewriting to joined derived table.
SEMIJOIN	Semi-join flattening.
DERIVED_TABLE	Rewrite to joined derived table.
SUBQ_EXISTS	Evaluate as EXISTS subquery (possibly after rewriting from another type)
SUBQ_MATERIALIZATION	Subquery materialization (HASH_SJ_ENGINE)
DELETED	Subquery has been deleted, probably because it was always false.

Function Documentation

IsItemInSubSelect()

bool IsItemInSubSelect

(

Item *

item

)

Returns whether the Item is an IN-subselect.

remove_in2exists_conds()

Item * remove_in2exists_conds

(

Item *

conds

)

Removes every predicate injected by IN->EXISTS.

This function is different from others:

• it wants to remove all traces of IN->EXISTS (for materialization)
• remove_subq_pushed_predicates() and remove_additional_cond() want to remove only the conditions of IN->EXISTS which index lookup already satisfies (they are just an optimization).

If there are no in2exists conditions, it will return the exact same pointer. If it returns a new Item, the old Item is left alone, so it can be reused in other settings.

Parameters

conds

Condition; may be nullptr.

Returns

new condition