Adding an extra condition to SQL query - mysql

Question

I'm trying to add an extra layer to my SQL query which looks like this:
SELECT
COUNT(*) totalCount
FROM
ts_room
WHERE
NOT EXISTS (
SELECT 1
FROM ts_roompref
JOIN ts_request
ON ts_roompref.request_id = ts_request.id
AND day_id = 1
AND period_id = 1
WHERE
ts_room.id = ts_roompref.room_id)
What I would like it to do is check that a row for the matching request.id does not exist in a table called ts_allocation. This is what I've attempted so far but it doesn't seem to be working:
SELECT
COUNT(*) totalCount
FROM
ts_room
WHERE
NOT EXISTS (
SELECT 1
FROM ts_roompref
JOIN ts_request
ON ts_roompref.request_id = ts_request.id
AND day_id = 1
AND period_id = 1
WHERE
ts_room.id = ts_roompref.room_id)
AND NOT EXISTS (
SELECT 1
FROM ts_roompref
JOIN ts_allocation
ON ts_roompref.request_id = ts_allocation.request_id
AND ts_allocation.status = "Allocated"
WHERE
ts_room.id = ts_roompref.room_id)
)
Any ideas? I've included my SQL Fiddle here: http://sqlfiddle.com/#!2/4540d/2

Answer 1

I think the problem has to do with the use of aliases: once I added alias names to the tables of your query, the query ran and returned some values (link to your modified sqlfiddle):
SELECT COUNT(*) totalCount
FROM ts_room rm
WHERE
NOT EXISTS (
SELECT 1
FROM ts_roompref rp
JOIN ts_request rq ON rp.request_id = rq.id AND day_id = 1 AND period_id = 1
WHERE rm.id = rp.room_id)
AND NOT EXISTS (
SELECT 1
FROM ts_roompref rp
JOIN ts_allocation a ON rp.request_id = a.request_id AND a.status = "Allocated"
WHERE rm.id = rp.room_id)