Excuse me if this has been asked before, but I tried looking for something similar but couldn’t find anything.

I have three tables: users, hobbies and user_hobbies (linking the first two). I want to calculate the similarity betweet two users based on their hobbies. For this, I need, first of all, two sets: User A hobbies and user B hobbies, which I can acquire with two simple queries. I have to calculate these two sets for other reasons too, in a php file, so they are available to me, in two arrays, for the next step:

I have to calculate their common hobbies (i.e. the intersection of the sets).

Idea #1: Having two arrays, I can calculate through some method the common elements.

Idea #2: I can make a third query (e.g. SELECT hobby FROM user_hobbies WHERE user_id IN ('uid_A', 'uid_B') GROUP BY hobby HAVING COUNT (*) = 2) and not bother myself.

I suppose my question is about performance. Is it quicker to calculate manually or are mysql queries much faster?