IN vs. JOIN with large rowsets

Question

I\'m wanting to select rows in a table where the primary key is in another table. I\'m not sure if I should use a JOIN or the IN operator in SQL Server 2005. Is there any si

Answer 1

Theory will only get you so far on questions like this. At the end of the day, you'll want to test both queries and see which actually runs faster. I've had cases where the JOIN version took over a minute and the IN version took less than a second. I've also had cases where JOIN was actually faster.

Personally, I tend to start off with the IN version if I know I won't need any fields from the subquery table. If that starts running slow, I'll optimize. Fortunately, for large datasets, rewriting the query makes such a noticeable difference that you can simply time it from Query Analyzer and know you're making progress.

Good luck!