Package 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.

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Interface
    Description
    static interface 
    BuiltInMetadata.DistinctRowCount.Handler
    Handler API.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final MetadataDef<BuiltInMetadata.DistinctRowCount>
    DEF
     

  • Method Summary

    Modifier and Type
    Method
    Description
    @Nullable Double
    getDistinctRowCount(ImmutableBitSet groupKey, @Nullable 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

  • Field Details

  • Method Details

    • getDistinctRowCount

      @Nullable Double getDistinctRowCount(ImmutableBitSet groupKey, @Nullable 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