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ALLBASE/SQL Performance and Monitoring Guidelines: HP 9000 Computer Systems > Chapter 3 Guidelines on Query Design

Using Fetch Unique Scans

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Fetch Unique is a special faster kind of index scan method which is automatically used when a predicate meets the following criteria:

There is exactly one EQUAL factor for each key column.
All factors must be exactly matching with a unique index.
No non-unique index columns occur in the WHERE clause.
The factors in the WHERE clause are ANDed together.
There are no indicator variables in the WHERE clause.
Data retrieval is done with a singleton SELECT, not a cursor. (A singleton operation is one in which only a single row qualifies.)

Providing a non-cursor SQL SELECT, UPDATE, or DELETE meets these criteria, it uses a Fetch Unique scan.

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