On Mar 8, 2004, at 5:40 AM, Chris wrote:
in a 'SELECT', does postgres read the 'WHERE' condition from left to right.
PostgreSQL (SQL in general?) does NOT define evaluation order (unlike programming languages like C).
It is a fairly well known optimization in Oracle (at least with the rule-based optimizer, and IIRC non-indexed clauses) to optimize the WHERE clause right to left.
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for example 1) select ... where a and b; 2) select ... where b and a;
1 and 2 will use the same cpu time or not ?
Depends on the problem. In theory the optimizer should find the best evaluation order after analyzing a and b.
Bye, Chris.
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Andrew Rawnsley President The Ravensfield Digital Resource Group, Ltd. (740) 587-0114 www.ravensfield.com
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