SELECT rooms.id, rooms.name
FROM rooms
WHERE rooms.id NOT IN
(
  SELECT reservations.room_id
  FROM reservations
  WHERE
  (
    ('2007-04-17' < sdate) AND ('2007-04-17' < edate < '2007-04-20')
    OR
    ('2007-04-17 >= sdate) AND ('2007-04-20' <= edate)
    OR
    ('2007-04-17 < sdate < '2007-04-20') AND ('2007-04-20' > edate)
  )
)