RelationalExpression objects in the same companion set are those that are inner-joined against each other; we use this to see in what parts of the graph we allow cycles. More...

#include <relational_expression.h>

Classes
struct	EqualTerm
	This represents equality between a set of fields, i.e. More...

Public Member Functions
	CompanionSet ()=default

	CompanionSet (THD *thd)

	CompanionSet (const CompanionSet &)=delete
	No copying. More...

CompanionSet &	operator= (const CompanionSet &)=delete

void	AddEquijoinCondition (THD *thd, const Item_func_eq &eq)
	Add the set of equal fields specified by 'func_eq'. More...

table_map	GetEqualityMap (const Field &field) const
	If 'field' is part of an equijoin predicate in this CompanionSet, return a table_map of the tables involved in that predicate. More...

std::string	ToString () const
	For tracing and debugging. More...

Private Types
using	FieldArray = Mem_root_array< const Field * >

Private Attributes
Mem_root_array< EqualTerm >	m_equal_terms
	The set of sets of fields in equijoin predicates in this companion set. More...

Detailed Description

RelationalExpression objects in the same companion set are those that are inner-joined against each other; we use this to see in what parts of the graph we allow cycles.

(Within companion sets, we are also allowed to add Cartesian products if we deem that an advantage, but we don't do it currently.) Tables may be alone in their companion sets. Companion sets are also used when calculating selectivity for equijoin predicates using multi-field indexes,

See also: EstimateEqualPredicateSelectivity()).

Member Typedef Documentation

◆ FieldArray

using CompanionSet::FieldArray = Mem_root_array<const Field *>

private

Constructor & Destructor Documentation

◆ CompanionSet() [1/3]

CompanionSet::CompanionSet ( )

default

◆ CompanionSet() [2/3]

CompanionSet::CompanionSet ( THD * thd )

inlineexplicit

◆ CompanionSet() [3/3]

CompanionSet::CompanionSet ( const CompanionSet & )

delete

No copying.

Member Function Documentation

◆ AddEquijoinCondition()

void CompanionSet::AddEquijoinCondition	(	THD *	thd,
		const Item_func_eq &	eq
	)

Add the set of equal fields specified by 'func_eq'.

◆ GetEqualityMap()

table_map CompanionSet::GetEqualityMap ( const Field & field ) const

If 'field' is part of an equijoin predicate in this CompanionSet, return a table_map of the tables involved in that predicate.

Otherwise, return 0.

◆ operator=()

CompanionSet & CompanionSet::operator= ( const CompanionSet & )

delete

◆ ToString()

std::string CompanionSet::ToString ( ) const

For tracing and debugging.

Returns: A string representation like "{{t1.f1, t2.f2}, {t2.f3, t3.f4}}".

Member Data Documentation

◆ m_equal_terms

Mem_root_array<EqualTerm> CompanionSet::m_equal_terms

private

The set of sets of fields in equijoin predicates in this companion set.

(

See also: EstimateEqualPredicateSelectivity() to see how this is utilized.) For example, if we have:

SELECT ... FROM t1, t2, t3 WHERE t1.x=t2.x AND t2.x=t3.x AND t2.y=t3.y

m_equal_terms will contain:

{{t1.x, t2.x, t3.x}, {t2.y, t3.y}}

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

sql/join_optimizer/relational_expression.h
sql/join_optimizer/relational_expression.cc

Classes

Public Member Functions

Private Types

Private Attributes