subselect_hash_sj_engine Class Reference

Compute an IN predicate via a hash semi-join. More...

#include <item_subselect.h>

Inheritance diagram for subselect_hash_sj_engine:

Public Member Functions
	subselect_hash_sj_engine (Item_in_subselect *in_predicate, Query_expression *unit_arg)
	~subselect_hash_sj_engine () override
bool	setup (THD *thd, const mem_root_deque< Item * > &tmp_columns)
	Create all structures needed for subquery execution using hash semijoin. More...
void	cleanup () override
	Cleanup performed after each execution. More...
bool	exec (THD *thd) override
	Execute a subquery IN predicate via materialization. More...
void	print (const THD *thd, String *str, enum_query_type query_type) override
	Print the state of this engine into a string for debugging and views. More...
enum_engine_type	engine_type () const override
TABLE *	get_table () const
const Index_lookup &	index_lookup () const
enum join_type	get_join_type () const
AccessPath *	root_access_path () const
void	create_iterators (THD *thd) override
Public Member Functions inherited from subselect_indexsubquery_engine
	subselect_indexsubquery_engine (TABLE *table, Table_ref *table_ref, const Index_lookup &ref, enum join_type join_type, Item_in_subselect *subs, Item *where, Item *having_arg)
virtual	~subselect_indexsubquery_engine ()=default

Private Types
enum	nulls_exist { NEX_IRRELEVANT_OR_FALSE = 0 , NEX_UNKNOWN = 1 , NEX_TRUE = 2 }
	Existence of inner NULLs in materialized table: By design, other values than IRRELEVANT_OR_FALSE are possible only if the subquery has only one inner expression. More...

Private Attributes
bool	is_materialized
bool	has_zero_rows = false
enum nulls_exist	mat_table_has_nulls
Query_expression *const	unit
unique_ptr_destroy_only< RowIterator >	m_iterator
AccessPath *	m_root_access_path
Query_result_interceptor *	saved_result {nullptr}
	Saved result object, must be restored after use. More...

Additional Inherited Members
Public Types inherited from subselect_indexsubquery_engine
enum	enum_engine_type { INDEXSUBQUERY_ENGINE , HASH_SJ_ENGINE }
Protected Attributes inherited from subselect_indexsubquery_engine
Query_result_union *	result = nullptr
TABLE *	table {nullptr}
	Table which is read, using one of eq_ref, ref, ref_or_null. More...
Table_ref *	table_ref {nullptr}
Index_lookup	ref
join_type	type {JT_UNKNOWN}
Item *	cond
ulonglong	hash
Item *	having
Item_in_subselect *	item

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.

Member Enumeration Documentation

nulls_exist

enum subselect_hash_sj_engine::nulls_exist

private

Existence of inner NULLs in materialized table: By design, other values than IRRELEVANT_OR_FALSE are possible only if the subquery has only one inner expression.

Enumerator
NEX_IRRELEVANT_OR_FALSE	none, or they don't matter
NEX_UNKNOWN	they matter, and we don't know yet if they exists
NEX_TRUE	they matter, and we know there exists at least one.

Constructor & Destructor Documentation

subselect_hash_sj_engine()

subselect_hash_sj_engine::subselect_hash_sj_engine ( Item_in_subselect *  in_predicate, Query_expression *  unit_arg  )

inline

~subselect_hash_sj_engine()

subselect_hash_sj_engine::~subselect_hash_sj_engine ( )

override

Member Function Documentation

cleanup()

void subselect_hash_sj_engine::cleanup ( )

overridevirtual

Cleanup performed after each execution.

Reimplemented from subselect_indexsubquery_engine.

create_iterators()

void subselect_hash_sj_engine::create_iterators ( THD *  thd )

overridevirtual

Reimplemented from subselect_indexsubquery_engine.

engine_type()

enum_engine_type subselect_hash_sj_engine::engine_type ( ) const

inlineoverridevirtual

Reimplemented from subselect_indexsubquery_engine.

exec()

bool subselect_hash_sj_engine::exec ( THD *  thd )

overridevirtual

Execute a subquery IN predicate via materialization.

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

Return values

true	if error
false	otherwise

Reimplemented from subselect_indexsubquery_engine.

get_join_type()

enum join_type subselect_hash_sj_engine::get_join_type ( ) const

inline

get_table()

TABLE * subselect_hash_sj_engine::get_table ( ) const

inline

index_lookup()

const Index_lookup & subselect_hash_sj_engine::index_lookup ( ) const

inline

print()

void subselect_hash_sj_engine::print ( const THD *  thd, String *  str, enum_query_type  query_type  )

overridevirtual

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

Reimplemented from subselect_indexsubquery_engine.

root_access_path()

AccessPath * subselect_hash_sj_engine::root_access_path ( ) const

inline

setup()

bool subselect_hash_sj_engine::setup	(	THD *	thd,
		const mem_root_deque< 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 Index_lookup objects to perform lookups into the indexed temporary table.

Parameters

thd	thread handle
tmp_columns	columns of temporary table

Note

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

Member Data Documentation

has_zero_rows

bool subselect_hash_sj_engine::has_zero_rows = false

private

is_materialized

bool subselect_hash_sj_engine::is_materialized

private

m_iterator

unique_ptr_destroy_only<RowIterator> subselect_hash_sj_engine::m_iterator

private

m_root_access_path

AccessPath* subselect_hash_sj_engine::m_root_access_path

private

mat_table_has_nulls

enum nulls_exist subselect_hash_sj_engine::mat_table_has_nulls

private

saved_result

Query_result_interceptor* subselect_hash_sj_engine::saved_result {nullptr}

private

Saved result object, must be restored after use.

unit

Query_expression* const subselect_hash_sj_engine::unit

private

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

• sql/item_subselect.h
• sql/item_subselect.cc