Re: ** SQL WHERE clause order

From: Yong Huang <yong321_at_yahoo.com>
Date: Tue, 04 Nov 2003 14:44:29 -0800
Message-ID: <F001.005D5930.20031104144429@fatcity.com>

Hi, Joshi,

The only hint that may affect the evaluation order in the WHERE clause is ORDERED_PREDICATES. But I don't know who actually got it to work. The chapter "Optimizer Hints" in Performance Tuning Guide talks about it. It also says if you don't have this hint, there's a certain order in which Oracle evaluates predicates in the WHERE clause. Not sure if that's true. You can try switching the predicates around and look at the execution plan for each.

Documentation is wrong in saying that you should be put that hint in the WHERE clause.

Yong Huang

• A Joshi <ajoshi977_at_yahoo.com> wrote:
  > Hi,
  > In a SQL statement I want a certain where clause to be done first. Is it
  > enough to list it first as follows or do I (and can I) do something else to
  > make it get checked first before other WHERE/AND clause are looked at. Thanks
  > :
  >
  > SELECT emp_id FROM emp
  > WHERE select_sen_emp_chk_first = 'Y'
  > AND dept = :dept
  > AND salary > :min_sal
  

  ---

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Author: Yong Huang
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Received on Tue Nov 04 2003 - 16:44:29 CST