Predicate manipulation

Db2 sometimes modifies existing predicates, generates extra predicates, or removes unneeded predicates to improve the chances that Db2 can select an efficient access path.

The goal of such transformations is most often to increase the likelihood that Db2 can select index-based access paths, which are often more efficient than other access methods.

In most cases, you do not have to do anything to take advantage of such predicate manipulations. However, you might see the transformed predicates in EXPLAIN data in DSN_PREDICAT_TABLE, and if you view formatted query text with a query tuning tools. You might also see access path changes that result from the predicate changes in PLAN_TABLE data and in access path diagrams.