To union or union all, that is the question

Question

I have two queries that I\'m UNIONing together such that I already know there will be no duplicate elements between the two queries. Therefore, UNION a

Answer 1

I see that you've tagged this question PERFORMANCE, so I assume that's your primary consideration.

UNION ALL will absolutely outperform UNION since SQL doesn't have to check the two sets for dups.

Unless you need SQL to perform the duplicate checking for you, always use UNION ALL.