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AskSQLTeam
Ask SQLTeam Question
0 Posts |
 Posted - 2006-09-12 : 18:50:54
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EveryNanoSecondCounts! writes "Hey, if I have a SELECT inside an SP kind of like this:CREATE PROC spThisAndThatSel ( @PMatch VARCHAR ) AS SELECT This, That, ThenSome FROM SOMETABLE WHERE (This = @PMatch OR @PMatch IS NULL) then, if the value of @PMatch is indeed NULL, would evaluation be faster if I put the @PMatch first (@PMatch IS NULL OR This = @PMatch), or will the optimizer realize that it doesn't need to evaluate the WHERE clause ?Thanx!" |
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LoztInSpace
Aged Yak Warrior
940 Posts |
Posted - 2006-09-12 : 19:57:56
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| The order of evaluation is not defined by how you write your query. The optimiser will decide that for you. I remember a few months ago there was another topic on this trying to do short circuit evaluation and someone proved it can sometimes change the order of evaluation. |
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Order Of evaluation in OR'ed subclauses