Using predicates efficiently

You can improve how DB2® processes SQL statements by following certain practices when writing predicates.

To use predicates most efficiently in SQL statements:

• Use stage 1 predicates whenever possible. Stage 1 predicates are better than stage 2 predicates because they disqualify rows earlier and reduce the amount of processing that is needed at stage 2. In terms of resource usage, the earlier a predicate is evaluated, the better.
• Write queries to evaluate the most restrictive predicates first. When predicates with a high filter factor are processed first, unnecessary rows are screened as early as possible, which can reduce processing cost at a later stage. However, a predicate's restrictiveness is only effective among predicates of the same type and at the same evaluation stage.