Re: EXPLAIN PLAN

From: PaulCinVT <paulcinvt_at_aol.com>
Date: 2000/05/09
Message-ID: <20000509103902.08158.00013693@nso-cg.aol.com>#1/1

The ORDERED_PREDICATES hint forces the optimizer to preserve the order of predicate evaluation, except for predicates used as index keys. Use this hint in the WHERE clause of SELECT statements.

If you do not use the ORDERED_PREDICATES hint, Oracle evaluates all predicates in the order specified by the following rules. Predicates:

Without user-defined functions, type methods, or subqueries are evaluated first, in the order specified in the WHERE clause.

With user-defined functions and type methods that have user-computed costs are evaluated next, in increasing order of their cost.

With user-defined functions and type methods without user-computed costs are evaluated next, in the order specified in the WHERE clause.

Not specified in the WHERE clause (for example, predicates transitively generated by the optimizer) are evaluated next.

With subqueries are evaluated last in the order specified in the WHERE clause.

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Note:
As mentioned, you cannot use the ORDERED_PREDICATES hint to preserve the order of predicate evaluation on index keys.

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See Also:
Oracle8i Concepts for a full discussion of ordered predicates.  

Paul in VT Received on Tue May 09 2000 - 00:00:00 CDT