Question

I’m currently trying to optimize an database by combining queries. But I keep hitting dead ends while optimizing an room availability query.

I have a room availability table where each records states the available number of rooms per date. It’s formatted like so:

• room_availability_id (PK)
• room_availability_rid (fk_room_id)
• room_availability_date (2011-02-11)
• room_availability_number (number of rooms available)

The trouble is getting a list of rooms that are available for EACH of the provided days. When I use IN() like so:

WHERE room_availability_date IN('2011-02-13','2011-02-14','2011-02-15')
AND room_availability_number > 0

If the 14th has availability 0 it still gives me the other 2 dates. But I only want that room_id when it is available on ALL three dates.

Please tell me there is a way to do this in MySQL other than querying each date/room/availability combination separately (that is what is done now 🙁 )

I tried all sorts of combinations, tried to use room_availability_date = ALL (…), tried some dirty repeating subqueries but to no avail.

Thank you in advance for any thoughts!

Answer 1

I think I can improve on a’r’s answer:

SELECT 
    room_availability_rid, count(*) n

WHERE room_availability_date IN ('2011-02-13','2011-02-14','2011-02-15')
  AND room_availability_number > 0

GROUP BY room_availability_rid 

HAVING n=3

Edit: This of course assumes that there is only one table entry per room per day. Is this a valid assumption?