How to get multiple counts with multiple joins using one SQL query? - mysql

Question

There is an error in my query and I would like some help. I have three tables
Rooms{id,number,name,type(ECO/LUX),active(0/1)}
Men{passport,roomid,status(YOUTH/ADULT)}
Women{passport,roomid,status(YOUTH/ADULT)}
**In each room there can be more than one woman or man.
I want to count how many women and men have the same room with roomid in (1,2,3), status='ADULT', type='LUX' and active=1. Therefore I need a result like this:
+----+--------+-----------+----------+------------+
| id | number | name | CountMen | CountWomen |
+----+--------+-----------+----------+------------+
| 1 | 23 | 1st suite | 2 | 4 |
| 3 | 4 | 2nd suite | 1 | 2 |
+----+--------+-----------+----------+------------+
SELECT id,number,name,
sum(case when Men.status='ADULT' then 1 else 0 end) as CountMen,
sum(case when Women.status='ADULT' then 1 else 0 end) as CountWomen
FROM Rooms left join Men
on Rooms.id=Men.roomid
left join Women on Room.id=Women.roomid where
(type='LUX') and (active=true) and (id in (1,2,3))
group by id;
The problem is that I get sometimes wrong results in the counters.

Answer 1

In a left join, conditions on the second table need to be in the on clause. It would help if you qualified all column names in the query.
However your problem is because you are getting a Cartesian product between the gender tables. This is definitely a case where gender segregation is not a good thing. You should have just one table for people (and this doesn't even bring up other issues with defining binary genders).
SELECT r.id, r.number, r.name,
(SELECT COUNT(*)
FROM men m
WHERE m.status = 'ADULT' AND r.id = m.roomid
) as CountMen,
(SELECT COUNT(*)
FROM women w
WHERE w.status = 'ADULT' AND r.id = w.roomid
) as CountWomen
FROM Rooms r
WHERE r.type = 'LUX' AND r.active = true AND r.id IN (1, 2, 3);
However, you should fix your data model so you have people rather than segregated gender tables.