org.apache.derby.impl.store.access.sort
Class UniqueWithDuplicateNullsMergeSort

java.lang.Object
  org.apache.derby.impl.store.access.sort.MergeSort
      org.apache.derby.impl.store.access.sort.UniqueWithDuplicateNullsMergeSort

All Implemented Interfaces:

Sort

final class UniqueWithDuplicateNullsMergeSort
extends MergeSort

This class extends and customizes MergeSort to support unique indexes with duplicate nulls. It overrides compare method to consider keypart - 1 parts of the keys while comparing (only for non null keys).

Field Summary

Fields inherited from class org.apache.derby.impl.store.access.sort.MergeSort

alreadyInOrder, columnOrdering, columnOrderingAscendingMap, columnOrderingMap, columnOrderingNullsLowMap, properties, sortBufferMax, sortBufferMin, sortObserver, template

Constructor Summary

UniqueWithDuplicateNullsMergeSort()

Method Summary

protected int

compare(DataValueDescriptor[] r1, DataValueDescriptor[] r2) Compares two keys.

Methods inherited from class org.apache.derby.impl.store.access.sort.MergeSort

checkColumnTypes, createMergeRun, doneInserting, doneScanning, doneScanning, drop, dropMergeRuns, initialize, open, openSortRowSource, openSortScan

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

UniqueWithDuplicateNullsMergeSort

UniqueWithDuplicateNullsMergeSort()

Method Detail

compare

protected int compare(DataValueDescriptor[] r1,
                      DataValueDescriptor[] r2)
               throws StandardException

Compares two keys. If all the parts of the keys are not null then the leading (keys.length - 1) parts are compared, else if no part of the key is null then all parts of the key are compared (keys.length). This behavior is useful for implementing unique constraints where multiple null values are allowed, but uniqueness must still be guaranteed for keys with no null values. In this case the leading parts of the key are the user key columns, while the last column is a system provided column which is guaranteed unique per base row.

Overrides:

compare in class MergeSort

Parameters:

r1 - keys

r2 - keys

Returns:

0 for duplicates non zero for distinct keys

Throws:

StandardException