How to create fast database queries

Archive for June 17th, 2009

Efficient EXISTS

Comments enabled. I *really* need your comment

In my previous article:

I compared efficiency of different methods to check for existence of a value in a subquery resultset.

These methods included IN and EXISTS predicates.

It was shown that in SQL Server, a poorly written EXISTS can be very slow, while an IN predicate is almost always efficiently optimized using one of the numerous SEMI JOIN methods.

However, a properly written EXISTS predicate can outperform IN.

Let's create a sample table and see how:
Read the rest of this entry »

Written by Quassnoi

June 17th, 2009 at 11:00 pm

Posted in SQL Server