Question

我在MySQL中有4个这样的表

第一张桌子：学生

id    Name       roll      final
1     vivek      22222     65000
2     abc        33333     50000

第二张表：折扣

id    gst_amount   roll 
1     5000         22222
2     6500         22222
3     15000        22222
4     6000         33333

第三张表：费用

id    amount       roll 
1     15000        22222
2     5000         22222
3     5000         33333

第四张表：pdc

id    amount       roll 
1     9250         22222
2     9250         22222

我想加入所有表，并希望将pdc和fee表中的金额和gst_amount表中的discount的总和与最后一列的值相加。

我尝试过此查询。

SELECT student.roll, final, SUM(discount.gst_amount) AS total, SUM(fee.amount) AS fee, SUM(pdc.amount) AS pdc  
FROM student 
LEFT JOIN discount on student.roll = discount.roll 
LEFT JOIN fee on fee.roll = student.roll 
LEFT JOIN pdc on pdc.roll = student.roll 
GROUP BY student.roll

这给了我这个输出。

roll      final     total     fee       pdc
22222     65000     106000    120000    110000
33333     50000     6000      5000      NULL

我想要这个输出。

roll      final     total     fee       pdc
22222     65000     26000     20000     18500
33333     50000     6000      5000      NULL

Answer 1

您的原始查询正在计算重复的总和值。
我认为您可以理解将count(1)列添加到原始查询中。
以下是我的输出。

mysql> SELECT student.roll, count(1) as count
    -> FROM student
    -> LEFT JOIN discount on student.roll = discount.roll
    -> LEFT JOIN fee on fee.roll = student.roll
    -> LEFT JOIN pdc on pdc.roll = student.roll
    -> GROUP BY student.roll
    -> ;
+-------+-------+
| roll  | count |
+-------+-------+
| 22222 |    12 |
| 33333 |     1 |
+-------+-------+
2 rows in set (0.00 sec)

基于这些，请按以下sql命令运行。
我认为此sql有一些改进点，但是我现在已经获得了您的预期结果。
我想总输出列中的26000是错误的，我认为26500是正确的。

SELECT 
    student.roll,
    final,
    SUM(discount.gst_amount) AS total,
    SUM(fee.amount) AS fee,
    SUM(pdc.amount) AS pdc
FROM
    student
LEFT JOIN
    (SELECT 
        roll, SUM(gst_amount) AS gst_amount
    FROM
        discount
    GROUP BY roll) AS discount ON discount.roll = student.roll
LEFT JOIN
    (SELECT 
        roll, SUM(amount) AS amount
    FROM
        fee
    GROUP BY roll) AS fee ON fee.roll = student.roll
LEFT JOIN
    (SELECT 
        roll, SUM(amount) AS amount
    FROM
        pdc
    GROUP BY roll) AS pdc ON pdc.roll = student.roll
GROUP BY student.roll

Answer 2

首先，对不起，我没有给您具体答案，但是我并不是最好的。您可以尝试通过子查询来完成。这将获得折扣表中每一卷的gst_amount的总和：

SELECT roll, SUM(gst_amount) AS gst_amount
FROM discount 
GROUP BY roll

如果您随后在当前查询中实现它，那么它可能会起作用。

sum函数返回错误值

2 个答案: