
7.3 Tools for Tuning Queries 191
Chapter 7
ORDERED_PREDICATES. Preserves SQL statement precedence
of evaluation, such as the sequence of comparisons in a WHERE
clause.
[NO_]UNNEST. Undoes subquery layers by allowing the optimizer
to attempt to merge subqueries into a calling query. This is probably
contrary to performance tuning of multiple layered SQL statements.
[NO_]PUSH_SUBQ. Resolves subqueries first or last (NO_).
Note: The most important thing to remember about using hints is that a
hint is only a suggestion to the optimizer, not an instruction. In other words,
the optimizer will ignore the hint if it thinks the hint is inappropriate.
7.3