What is best practice with IF Exists

[mjp483]

I want to run an update based on whether a condition exists. To get the condition I run a query written like

IF Exists (select 1 from Table a join Table b on a.id = b.id)

Update Table A

The select query returns 300 or so results as 1, is there a better practice so the condition is met before all 300 results are retrieved...maybe something more efficient to kick off the update once the very first record is found? Or is it already? Thanks

 

[vongrunt]

Who says SELECT query returns 300 results? :X

------
"There's a man... He's bald and wears a short-sleeved shirt, and somehow he's very important to me. I think his name is Homer."
(Jack O'Neill, Stargate)

 

[mjp483]

In query analyzer I run the select statement and it returns 300 1's......

 

[vongrunt]

Yes, but EXISTS() tells optimizer to stop subquery execution after first value found.

So tehnically - even if * is used instead of 1, it shouldn't matter (for SQL2k server).



------
"There's a man... He's bald and wears a short-sleeved shirt, and somehow he's very important to me. I think his name is Homer."
(Jack O'Neill, Stargate)

 

[mjp483]

That is the assurance I was looking for...thanks.