MySQl Query giving wrong result - mysql

Question

Select * from YogaTimeTable;
Delete
from YogaTimeTable
Where RoomNum IN (select tt.RoomNum
from YogaRooms r,
YogaTypes t,
YogaTimeTable tt
where r.RoomNum = tt.roomNum
and ((r.RoomCapacity * t.ClassPrice) - (r.CostPerHour * tt.duration / 60)) < 200);
Select * from YogaTimeTable;
The goal is to delete any classes from the timetable that can make less than $200 profit. To calculate the profitability of each class, multiply the roomcapacity by the classprice and then subtract the cost of the room. To calculate the cost of the room multiply the costperhour by the duration divided by 60.
but it isn't giving the right result, can someone tell me where I made my mistake. Thanks. The tables are attached.

Answer 1

To me it looks like you have two problems.
A cross join between t and tt exists and should be resolved.
You're attempting to delete based on an incomplete or partial key of YogaTimeTable. The Unique Key of YogaTimeTable appears to be YogaID, StartTime,Day and RoomNum. I say this because the same yoga type could be in the same room at the same time on a different day, or in the same room on the same day at different start times. Thus I think the unique key for YogaTimeTable is a composite key of those 4 fields. So when deleting you need to use the complete key, not a partial key.
So this would result in.
.
DELETE FROM YogaTimeTable
WHERE exists
(SELECT 1
FROM YogaRooms r
INNER JOIN YogaTimeTable tt
on r.RoomNum = tt.roomNum
INNER JOIN YogaTypes t
on tt.YogaID = t.YogaID
WHERE YogaTimeTable.YogaID = TT.YogaID
and YogaTimeTable.RoomNum = TT.RoomNum
and YogaTimeTable.StartTime = TT.StartTime
and YogaTimeTable.Day = TT.Day
and ((r.RoomCapacity * t.ClassPrice) - (r.CostPerHour * tt.duration / 60)) < 200);
According to: I can use a correlated subquery to delete I just can't alias the table.... https://bugs.mysql.com/bug.php?id=2920

Answer 2

Profitability of all classes...
select ytt.YogaID,
ytt.Day,
ytt.StartTime,
ytt.RoomNum,
yt.ClassPrice,
ifnull(ytt.Duration,0) as Duration,
ifnull(yr.CostPerHour,0) as CostPerHour,
ifnull(yr.RoomCapacity,0) as RoomCapacity,
round( ifnull(yr.RoomCapacity,0)*yt.ClassPrice
- (ifnull(yr.CostPerHour,0)*ifnull(ytt.Duration,0)/60)
, 2) as Profitability
from YogaTypes yt
left join YogaTimeTable ytt on (ytt.YogaID=yt.YogaID)
left join YogaRooms yr on (yr.RoomNum=ytt.RoomNum);
+--------+-----------+-----------+---------+------------+----------+-------------+--------------+---------------+
| YogaID | Day | StartTime | RoomNum | ClassPrice | Duration | CostPerHour | RoomCapacity | Profitability |
+--------+-----------+-----------+---------+------------+----------+-------------+--------------+---------------+
| DRU | Wednesday | 10:30:00 | 1 | 18.50 | 60.00 | 100.00 | 20 | 270.00 |
| DRU | Tuesday | 17:00:00 | 2 | 18.50 | 90.00 | 50.00 | 10 | 110.00 |
| SUN | Monday | 07:30:00 | 3 | 18.00 | 60.00 | 150.00 | 25 | 300.00 |
| HAT | Tuesday | 07:30:00 | 4 | 20.00 | 90.00 | 70.00 | 15 | 195.00 |
| HAT | Monday | 18:30:00 | 4 | 20.00 | 60.00 | 70.00 | 15 | 230.00 |
| NULL | NULL | NULL | NULL | 17.00 | 0.00 | 0.00 | 0 | 0.00 |
+--------+-----------+-----------+---------+------------+----------+-------------+--------------+---------------+
6 rows in set (0.00 sec)
The classes with profitability less than desired...
select ytt.YogaID,
ytt.Day,
ytt.StartTime,
ytt.RoomNum
from YogaTypes yt
left join YogaTimeTable ytt on (ytt.YogaID=yt.YogaID)
left join YogaRooms yr on (yr.RoomNum=ytt.RoomNum)
where ifnull(yr.RoomCapacity,0)*yt.ClassPrice
- (ifnull(yr.CostPerHour,0)*ifnull(ytt.Duration,0)/60) < 200;
+--------+---------+-----------+---------+
| YogaID | Day | StartTime | RoomNum |
+--------+---------+-----------+---------+
| DRU | Tuesday | 17:00:00 | 2 |
| HAT | Tuesday | 07:30:00 | 4 |
| NULL | NULL | NULL | NULL |
+--------+---------+-----------+---------+
3 rows in set (0.00 sec)
Now to delete the undesirable sessions...
delete tt.*
from YogaTimeTable tt,
(select ytt.YogaID,
ytt.Day,
ytt.StartTime,
ytt.RoomNum
from YogaTypes yt
left join YogaTimeTable ytt on (ytt.YogaID=yt.YogaID)
left join YogaRooms yr on (yr.RoomNum=ytt.RoomNum)
where ifnull(yr.RoomCapacity,0)*yt.ClassPrice
- (ifnull(yr.CostPerHour,0)*ifnull(ytt.Duration,0)/60) < 200
) as unprof
where tt.YogaID=unprof.YogaID
and tt.RoomNum=unprof.RoomNum
and tt.Day=unprof.Day
and tt.StartTime=unprof.StartTime;
Query OK, 2 rows affected (0.00 sec)