org.apache.derby.catalog
Interface Statistics

All Known Implementing Classes:

StatisticsImpl

public interface Statistics

This interface is used in the column SYS.SYSSTATISTICS.STATISTICS. It encapsulates information collected by the UPDATE STATISTICS command and is used internally by the Derby optimizer to estimate cost and selectivity of different query plans.

Method Summary

long	getRowEstimate() Returns the estimated number of rows in the index.
double	selectivity(java.lang.Object[] predicates)

Method Detail

getRowEstimate

long getRowEstimate()

Returns the estimated number of rows in the index.

Returns:

Number of rows.

selectivity

double selectivity(java.lang.Object[] predicates)

Returns:

the selectivity for a set of predicates.