io.prestosql.sql.planner.iterative.rule

Class PushAggregationThroughOuterJoin

java.lang.Object

io.prestosql.sql.planner.iterative.rule.PushAggregationThroughOuterJoin

All Implemented Interfaces:

Rule<AggregationNode>

public class PushAggregationThroughOuterJoin
extends Object
implements Rule<AggregationNode>

This optimizer pushes aggregations below outer joins when: the aggregation is on top of the outer join, it groups by all columns in the outer table, and the outer rows are guaranteed to be distinct.

When the aggregation is pushed down, we still need to perform aggregations on the null values that come out of the absent values in an outer join. We add a cross join with a row of aggregations on null literals, and coalesce the aggregation that results from the left outer join with the result of the aggregation over nulls.

Example:

 - Filter ("nationkey" > "avg")
  - Aggregate(Group by: all columns from the left table, aggregation:
    avg("n2.nationkey"))
      - LeftJoin("regionkey" = "regionkey")
          - AssignUniqueId (nation)
              - Tablescan (nation)
          - Tablescan (nation)
 

Is rewritten to:

 - Filter ("nationkey" > "avg")
  - project(regionkey, coalesce("avg", "avg_over_null")
      - CrossJoin
          - LeftJoin("regionkey" = "regionkey")
              - AssignUniqueId (nation)
                  - Tablescan (nation)
              - Aggregate(Group by: regionkey, aggregation:
                avg(nationkey))
                  - Tablescan (nation)
          - Aggregate
            avg(null_literal)
              - Values (null_literal)
 

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
PushAggregationThroughOuterJoin()

Method Summary

Modifier and Type	Method and Description
Rule.Result	apply(AggregationNode aggregation, Captures captures, Rule.Context context)
Pattern<AggregationNode>	getPattern() Returns a pattern to which plan nodes this rule applies.
boolean	isEnabled(Session session)

Methods inherited from class java.lang.Object

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

Constructor Detail

PushAggregationThroughOuterJoin

public PushAggregationThroughOuterJoin()

Method Detail

getPattern

public Pattern<AggregationNode> getPattern()

Description copied from interface: Rule

Returns a pattern to which plan nodes this rule applies.

Specified by:

getPattern in interface Rule<AggregationNode>

isEnabled

public boolean isEnabled(Session session)

Specified by:

isEnabled in interface Rule<AggregationNode>

apply

public Rule.Result apply(AggregationNode aggregation,
                         Captures captures,
                         Rule.Context context)

Specified by:

apply in interface Rule<AggregationNode>