io.prestosql.sql.planner.iterative.rule

Class TransformCorrelatedScalarAggregationToJoin

java.lang.Object

io.prestosql.sql.planner.iterative.rule.TransformCorrelatedScalarAggregationToJoin

All Implemented Interfaces:

Rule<LateralJoinNode>

public class TransformCorrelatedScalarAggregationToJoin
extends Object
implements Rule<LateralJoinNode>

Scalar aggregation is aggregation with GROUP BY 'a constant' (or empty GROUP BY). It always returns single row.

This optimizer rewrites correlated scalar aggregation subquery to left outer join in a way described here: https://github.com/prestosql/presto/wiki/Correlated-subqueries

From:

 - LateralJoin (with correlation list: [C])
   - (input) plan which produces symbols: [A, B, C]
   - (subquery) Aggregation(GROUP BY (); functions: [sum(F), count(), ...]
     - Filter(D = C AND E > 5)
       - plan which produces symbols: [D, E, F]
 

to:

 - Aggregation(GROUP BY A, B, C, U; functions: [sum(F), count(non_null), ...]
   - Join(LEFT_OUTER, D = C)
     - AssignUniqueId(adds symbol U)
       - (input) plan which produces symbols: [A, B, C]
     - Filter(E > 5)
       - projection which adds non null symbol used for count() function
         - plan which produces symbols: [D, E, F]
 

Note that only conjunction predicates in FilterNode are supported

Nested Class Summary

Nested classes/interfaces inherited from interface io.prestosql.sql.planner.iterative.Rule

Rule.Context, Rule.Result

Constructor Summary

Constructors

Constructor and Description
TransformCorrelatedScalarAggregationToJoin(FunctionRegistry functionRegistry)

Method Summary

Modifier and Type	Method and Description
Rule.Result	apply(LateralJoinNode lateralJoinNode, Captures captures, Rule.Context context)
Pattern<LateralJoinNode>	getPattern() Returns a pattern to which plan nodes this rule applies.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface io.prestosql.sql.planner.iterative.Rule

isEnabled

Constructor Detail

TransformCorrelatedScalarAggregationToJoin

public TransformCorrelatedScalarAggregationToJoin(FunctionRegistry functionRegistry)

Method Detail

getPattern

public Pattern<LateralJoinNode> getPattern()

Description copied from interface: Rule

Returns a pattern to which plan nodes this rule applies.

Specified by:

getPattern in interface Rule<LateralJoinNode>

apply

public Rule.Result apply(LateralJoinNode lateralJoinNode,
                         Captures captures,
                         Rule.Context context)

Specified by:

apply in interface Rule<LateralJoinNode>