Indexable and non-indexable predicates

An indexable predicate can match index entries; predicates that cannot match index entries are said to be non-indexable.

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To make your queries as efficient as possible, you can use indexable predicates in your queries and create suitable indexes on your tables. Indexable predicates allow the possible use of a matching index scan, which is often a very efficient access path.

Indexable predicates might or might not become matching predicates of an index; depending on the availability of indexes and the access path that DB2® chooses at bind time.

For example, if the employee table has an index on the column LASTNAME, the following predicate can be a matching predicate:

SELECT * FROM DSN8A10.EMP WHERE LASTNAME = 'SMITH';

In contrast, the following predicate cannot be a matching predicate, because it is not indexable.

SELECT * FROM DSN8A10.EMP WHERE SEX <> 'F';

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