MySQl Query给出错误结果

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; 

目标是从时间表中删除任何可以赚取少于200美元利润的类。要计算每个班级的收益率，请将房间容量乘以班级价格，然后减去房间的费用。要计算房间的成本乘以持续时间除以60. 乘以costperhour但它没有给出正确的结果，有人可以告诉我，我犯了我的错误。谢谢。表格被附上。

Answer 1

对我来说，它看起来像你有两个问题。

1. t和tt之间的交叉连接存在，应该解决。
2. 您正试图根据YogaTimeTable的不完整或部分关键字进行删除。 YogaTimeTable的独特密钥出现成为YogaID，StartTime，Day和RoomNum。我这样说是因为同一个瑜伽类型可以在不同的日子同时在同一个房间里，或者在不同的开始时间在同一天的同一个房间里。因此，我认为YogaTimeTable的唯一关键是这四个领域的复合关键。所以在删除时，你需要使用完整的密钥，而不是部分密钥。

所以这会导致。 。

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); 

据：我可以使用相关子查询删除我不能别名表.... https://bugs.mysql.com/bug.php?id=2920

Answer 2

各阶层的盈利能力......

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) 

的利润低于预期的类别...

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) 

现在删除不需要的rable 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)