Package io.prestosql.sql.planner

Class EqualityInference

  • public class EqualityInference
extends Object
    Makes equality based inferences to rewrite Expressions and generate equality sets in terms of specified symbol scopes

    • Method Detail

      • rewrite

        public Expression rewrite​(Expression expression,
                          Set<Symbol> scope)
        Attempts to rewrite an Expression in terms of the symbols allowed by the symbol scope given the known equalities. Returns null if unsuccessful.

      • generateEqualitiesPartitionedBy

        public EqualityInference.EqualityPartition generateEqualitiesPartitionedBy​(Set<Symbol> scope)
        Dumps the inference equalities as equality expressions that are partitioned by the symbolScope. All stored equalities are returned in a compact set and will be classified into three groups as determined by the symbol scope:
        1. equalities that fit entirely within the symbol scope
        2. equalities that fit entirely outside of the symbol scope
        3. equalities that straddle the symbol scope
         Example:
   Stored Equalities:
     a = b = c
     d = e = f = g

   Symbol Scope:
     a, b, d, e

   Output EqualityPartition:
     Scope Equalities:
       a = b
       d = e
     Complement Scope Equalities
       f = g
     Scope Straddling Equalities
       a = c
       d = f

      • isInferenceCandidate

        public static boolean isInferenceCandidate​(Metadata metadata,
                                           Expression expression)
        Determines whether an Expression may be successfully applied to the equality inference

      • nonInferrableConjuncts

        public static List<Expression> nonInferrableConjuncts​(Metadata metadata,
                                                      Expression expression)
        Provides a convenience Iterable of Expression conjuncts which have not been added to the inference