Question

I have two tables: users and user_depts. Let’s say (for this question) that users only has an ‘id’ column, and user_depts has 2: ‘uid’ and ‘did’.

I am looking for an SQL line that will return all the user IDs for all the departments with which a given user ID (let’s say 7, though this’ll come dynamically from PHP) is associated.

What I’ve tried is:

SELECT id FROM users, user_depts
WHERE users.id = user_depts.uid
AND user_depts.uid = 7

But of course this does nothing but return 7. I think I might have to join the table to itself, but I only know the shortcut syntax for joining, and it doesn’t seem to be sufficient. Any pointers would be greatly appreciated!

Answer 1

Use EXISTS:

SELECT uid FROM user_depts
WHERE EXISTS (
  SELECT * FROM user_depts a
  WHERE uid = 7 AND a.did = user_depts.did
)