SQL, how to get rows by known value that have the same value in another column?

Question

I need your help.

I have a table like this:

So I want to search for a specific thread. I have two user_id values and I want the rows returned where the user_id is one of the two and the thread_id is the same.

Let's say, Johnny(1) has a thread with Mark(2). Now I know Johny and Mark but I want to get the thread_id of the thread they have in common.

I'd appreciate a SQL hint, but if you know Laravel and Eloquent, that would be even better.

Answer 1

In SQL:

SELECT thread_id
FROM mytable
WHERE user_id IN (1, 2)
GROUP BY thread_id
HAVING COUNT(DISTINCT user_id) = 2