So You Wanna Be An SQL Server DBA...

[GaryMazzone]

I use them but they really need to be thought about. Would you want to run the correlated query (which runs against every row) if you were pulling a record set with millions of rows? I would say this would be a problem.

[szlamany]

I'm going to go out on a limb here and suggest that the correlated query - in an EXISTS() function - never returns any rows. It just makes it as far as the INDEX SEEK/SCAN or TABLE SCAN - finds that a row exists - and then it's job is done.