Need help with a MySQL query

Question

Please help me with this MySQL query. I've been on it for long enough. Perhaps it needs a fresh pair of eyes.

Two tables: locks and sessions

locks
--------------
id session_id
--------------
1  sajf4$Jf9422jd
2  2jf*4j2okg9092
3  J8j4j4ffss93o2
------------------

sessions
-------------------------
id              user_id
-------------------------
sajf4$Jf9422jd  14
J8j4j4ffss93o2  14
2jf*4j2okg9092  21
-------------------------

I want to delete all rows in locks where user_id of session = 14

Answer 1

DELETE FROM locks 
WHERE session_id IN (SELECT id FROM sessions WHERE user_id = 14)

Answer 2

DELETE FROM locks WHERE session_id = (SELECT id FROM sessions WHERE user_id = 14);

Answer 3

delete from locks where session_id in (select_id from sessions where user_id =14)

Answer 4

Another way without a subquery:

delete from locks using locks join sessions on sessions.id=locks.session_id where sessions.user_id=14

Answer 5

DELETE locks, sessions FROM locks INNER JOIN sessions WHERE locks.session_id=sessions.id;