This class represents a subquery contained in some subclass of Item_subselect,. More...

#include <item.h>

Public Types
enum class	Strategy : char { kMaterializable , kNonMaterializable , kIndependentSingleRow }
	The strategy for executing the subquery. More...

Public Attributes
AccessPath *	path
	The root path of the subquery. More...

Strategy	strategy
	The strategy for executing the subquery. More...

int	row_width
	The width (in bytes) of the subquery's rows. More...

Detailed Description

This class represents a subquery contained in some subclass of Item_subselect,.

See also: FindContainedSubqueries().

Member Enumeration Documentation

◆ Strategy

enum class ContainedSubquery::Strategy : char

strong

The strategy for executing the subquery.

Enumerator

kMaterializable

An independent subquery that is materialized, e.g.

: "SELECT * FROM tab WHERE field IN <independent subquery>". where 'independent subquery' does not depend on any fields in 'tab'. (This corresponds to the Item_in_subselect class.)

kNonMaterializable

A subquery that is reevaluated for each row, e.g.

: "SELECT * FROM tab WHERE field IN <dependent subquery>" or "SELECT * FROM tab WHERE field = <dependent subquery>". where 'dependent subquery' depends on at least one field in 'tab'. Alternatively, the subquery may be independent of 'tab', but contain a non-deterministic function such as 'rand()'. Such subqueries are also required to be reevaluated for each row.

kIndependentSingleRow

An independent single-row subquery that is evaluated once, e.g.

: "SELECT * FROM tab WHERE field = <independent single-row subquery>". (This corresponds to the Item_singlerow_subselect class.)

Member Data Documentation

◆ path

AccessPath* ContainedSubquery::path

The root path of the subquery.

◆ row_width

int ContainedSubquery::row_width

The width (in bytes) of the subquery's rows.

For variable-sized values we use Item.max_length (but cap it at kMaxItemLengthEstimate).

See also: kMaxItemLengthEstimate and; Item_in_subselect::get_contained_subquery().

◆ strategy

Strategy ContainedSubquery::strategy