Short Circuit?

[jararaca]

When you use an OR, will SQL Server evaluate the left part before it determines it is necessary to evaluate the right part? You know what I mean? For example:

a = 1 or b = 2

If a = 1, it's not necessary to evaluate the b = 2 part. Is SQL Server smart enough to figure this kind of thing out?

Thanks.

 

[DotNetGnat]

in case of OR condition...both the parts are evaluated....even if a=1 not true...b=2 will be checked..if that is true the whole condition becomes true...

-DNG

 

[vongrunt]

Imagine the following clause:

WHERE <expression1> OR <expression2>

If server takes table/clustered scan then yes, it will not evaluate ex2 if exp1 returns true. But what if server can optimize exp1 and exp2 separately and then UNION both results (internally)? Then Boolean short-circuit would become an "obstacle" in exec plan.

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