Package io.prestosql.sql.planner.iterative.rule

Class TransformCorrelatedScalarAggregationToJoin

  • public class TransformCorrelatedScalarAggregationToJoin
extends Object
    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: 

     - CorrelatedJoin (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]
     - projection which adds non null symbol used for count() function
       - Filter(E > 5)
         - plan which produces symbols: [D, E, F]

    Note that only conjunction predicates in FilterNode are supported

    • Constructor Detail

      • TransformCorrelatedScalarAggregationToJoin

        public TransformCorrelatedScalarAggregationToJoin​(Metadata metadata)

    • Method Detail

      • rules

        public Set<Rule<?>> rules()