SQL select with complicated conditions - mysql

Question

I'm banging my head with some SQL query and pretty much the logic behind it.
Let's assume we have these tables:
Table hotels
+----+---------+
| id | name |
+----+---------+
| 1 | Hotel A |
+----+---------+
Table hotel_rooms
+----+----------+-----------+
| id | hotel_id | room_type |
+----+----------+-----------+
| 1 | 1 | dbl | <- can be used as A,B,C,D,E,F
| 2 | 1 | dbl | <- can be used as B,C,D,E,F
| 3 | 1 | sng | <- can be used as A
| 4 | 1 | trp | <- can be used as D,E,F
+----+----------+-----------+
Table hotel_room_usages
+----+---------+-------+
| id | room_id | usage |
+----+---------+-------+
| 1 | 1 | B |
| 2 | 1 | C |
| 3 | 1 | A |
| 4 | 1 | D |
| 5 | 1 | E |
| 6 | 1 | F |
| 7 | 2 | B |
| 8 | 2 | C |
| 9 | 2 | D |
| 10 | 2 | E |
| 11 | 2 | F |
| 12 | 3 | A |
| 13 | 4 | D |
| 14 | 4 | E |
| 15 | 4 | F |
+----+---------+-------+
If I search for 2 rooms with usage A or 3 rooms with usage D as separate queries the result should be Hotel A with the corresponding IDs of the rooms.
The problem is if I search for 2 rooms with usage A and 3 rooms with usage D at the same time it returns also the hotel A because it doesn't count that some rooms can be used as A and D.
The rooms should be unique /total of 5/. The current example should not return a result because there are total of 4 rooms in the hotel.

Answer 1

does this help?
-- two rooms with usage a
select id from hotel_room_usages where usage = 'a'
-- three rooms with usage d
select id from hotel_room_usages where usage = 'd'
-- count of rooms with either
select count(distinct(room_id)) from hotel_room_usages where usage in ('a','d')

Answer 2

SELECT h.name AS hotel_name
, q.*
FROM
(
SELECT r.hotel_id
, COUNT(DISTINCT CASE WHEN ruA.room_id IS NOT NULL AND ruD.room_id IS NULL THEN ruA.room_id END) AS TotalRoomsOnlyA
, COUNT(DISTINCT CASE WHEN ruD.room_id IS NOT NULL AND ruA.room_id IS NULL THEN ruD.room_id END) AS TotalRoomsOnlyD
, COUNT(DISTINCT CASE WHEN ruA.room_id IS NOT NULL AND ruD.room_id IS NOT NULL THEN r.id END) AS TotalRoomsAandD
, COUNT(DISTINCT r.id) AS TotalRoomsAorD
FROM hotel_rooms AS r
LEFT JOIN hotel_room_usages AS ruA ON (ruA.room_id = r.id AND ruA.usage = 'A')
LEFT JOIN hotel_room_usages AS ruD ON (ruD.room_id = r.id AND ruD.usage = 'D')
WHERE (ruA.room_id IS NOT NULL OR ruD.room_id IS NOT NULL)
GROUP BY r.hotel_id
) q
JOIN hotels AS h ON (h.id = q.hotel_id)
CROSS JOIN (SELECT 2 AS a, 3 AS d) AS n
WHERE TotalRoomsAorD >= (a+d)
AND (
((TotalRoomsOnlyA + TotalRoomsAandD) >= a AND TotalRoomsOnlyD >= d) OR
(TotalRoomsOnlyA >= d AND (TotalRoomsOnlyD + TotalRoomsAandD) >= d) OR
((TotalRoomsOnlyA + TotalRoomsAandD/2) >= a AND (TotalRoomsOnlyD + TotalRoomsAandD/2) >= d)
)
ORDER BY h.name;
Test on db<>fiddle here