T-SQL: Ensure expression evaluation order in WHERE statement

Question

I'm sure someone can quickly solve this for me. I'm sure I'm not the first to ask this question, but i didn't find anything similar yet.

Having the following WHERE statement:

WHERE boolean_expression1 OR boolean_expression2 OR subquery_count > 0

Is this executed this way?:

I mean: Is the subquery only executed if the preceeding expressions both are false? And if not, is there any way I can ensure this?

Because the subquery could be quite expensive in my case.

Thx in advance, Chris

SQL Server does **NOT** make any promises about the order of evaluation - and you cannot force any order, either. — marc_s, Jun 14 '13 at 08:39
How about CASE WHEN-expressions? Could you imagine a statement for this OR example: WHERE (@GlobalSearch = 1 OR @SomeCount = 0 OR (subquery) >= @SomeCount) — Christian Kahlau, Jun 14 '13 at 08:43
check the execution plan. http://stackoverflow.com/questions/7359702/how-do-i-obtain-a-query-execution-plan — Eric213, Jun 14 '13 at 08:46

score 0 · Accepted Answer · answered Jun 14 '13 at 08:47

0

WHERE case when boolean_expression1 then 1
else case when boolean_expression2 then 1
else when subquery_count > 0 then 1 end = 1

answered Jun 14 '13 at 08:47

t-clausen.dk

1 Answers1