mysql: select all items from table A if not exist in table B

Question

I am having problem with selecting values from table a (id, room_name) where there are no corresponding events in table b (room_id, room_start, room_finish)

my query

Answer 1

You are missing to use only the events from that room. That is done by matching the id.

SELECT id, room_name FROM rooms r
WHERE NOT EXISTS 
(SELECT * FROM room_events re
      WHERE r.id = re.room_id AND
      room_start BETWEEN '1294727400' AND '1294729200' 
      OR 
      room_finish BETWEEN '1294727400' AND '1294729200')