Package 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.
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Method Summary
Modifier and TypeMethodDescriptionlong
Returns the estimated number of rows in the index.double
selectivity
(Object[] predicates)
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Method Details
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getRowEstimate
long getRowEstimate()Returns the estimated number of rows in the index.- Returns:
- Number of rows.
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selectivity
- Returns:
- the selectivity for a set of predicates.
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