org.apache.calcite.rel.metadata

Interface BuiltInMetadata.DistinctRowCount

All Superinterfaces:

Metadata

Enclosing class:

BuiltInMetadata

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 Summary

Methods

Modifier and Type	Method and Description
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.

Methods inherited from interface org.apache.calcite.rel.metadata.Metadata

rel

Method Detail

getDistinctRowCount

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").

Parameters:

groupKey - column mask representing group by columns

predicate - pre-filtered predicates

Returns:

distinct row count for groupKey, filtered by predicate, or null if no reliable estimate can be determined