Interface BuiltInMetadata.DistinctRowCount

  • All Superinterfaces:
    All Known Subinterfaces:
    Enclosing class:

    public static interface BuiltInMetadata.DistinctRowCount
    extends Metadata
    Metadata about the number of distinct rows returned by a set of columns in a relational expression.
    • Method Detail

      • getDistinctRowCount

        java.lang.Double getDistinctRowCount​(ImmutableBitSet groupKey,
                                             RexNode predicate)
        Estimates the number of rows which would be produced by a GROUP BY on the set of columns indicated by groupKey, where the input to the GROUP BY has been pre-filtered by predicate. This quantity (leaving out predicate) is often referred to as cardinality (as in gender being a "low-cardinality column").
        groupKey - column mask representing group by columns
        predicate - pre-filtered predicates
        distinct row count for groupKey, filtered by predicate, or null if no reliable estimate can be determined