org.eigenbase.stat

Interface RelStatColumnStatistics

public interface RelStatColumnStatistics

This interface provides results based on column statistics. It may be used to summarize the results of applying a predicate to a column of a relational expression. Alternatively, it may be used to summarize aspects of the entire column.

Method Summary

Methods

Modifier and Type	Method and Description
Double	getCardinality() Estimates the number of distinct values returned from a relational expression that satisfy a given condition.
Double	getSelectivity() Estimates the percentage of a relational expression's rows which satisfy a given condition.

Method Detail

getSelectivity

Double getSelectivity()

Estimates the percentage of a relational expression's rows which satisfy a given condition. This corresponds to the metadata query RelMetadataQuery.getSelectivity(org.eigenbase.rel.RelNode, org.eigenbase.rex.RexNode).

Returns:

an estimated percentage from 0.0 to 1.0 or null if no reliable estimate can be determined

getCardinality

Double getCardinality()

Estimates the number of distinct values returned from a relational expression that satisfy a given condition.

Returns:

an estimate of the distinct values of a predicate or null if no reliable estimate can be determined