NOT IN does not produce same results as NOT EXISTS

Question

These are rather basic statements. I have a list of graphics which are linked to items in another table. I want to check how many of the graphics are not in use and can theoreti

Answer 1

NOT IN with a subquery has strange behavior. If any row in the subquery returns a NULL value, then no rows are returned. This is due to following the strict semantics of NULL (which means: "I don't know if they are equal").

NOT EXISTS behaves as you would expect. For this reason, I recommend never using NOT IN with a subquery. Always use NOT EXISTS.