org.eigenbase.stat
Interface RelStatColumnStatistics

All Known Implementing Classes:

FarragoColumnHistogram

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.

Version:

$Id: //open/dev/farrago/src/org/eigenbase/stat/RelStatColumnStatistics.java#7 $

Author:

John Pham

Method Summary

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