MySQL连接查询中的GROUB BY

有两张桌子。第一个存储每个用户的费用

+----+----+----+
| id |uid |fee |
+----+----+----+
| 1  |P001|100 |
+----+----+----+
| 2  |P002|200 |
+----+----+----+
| 3  |P003|250 |
+----+----+----+
| 4  |P004|100 |
+----+----+----+
| 5  |P001|200 |
+----+----+----+
| 6  |P002|200 |
+----+----+----+
| 7  |P003|250 |
+----+----+----+
| 8  |P004|100 |
+----+----+----+

第二个存储用户分类

+----+-----+
|uid |class|
+----+-----+
|P001| 1   |
+----+-----+
|P002| 1   |
+----+-----+
|P003| 2   |
+----+-----+
|P004| 3   |
+----+-----+

我想显示他们的总和，按类别分组如下

1 - 700
2 - 500
3 - 200

我应该如何编写这个SQL查询？提前感谢。

试试这个：

SELECT class, SUM(fee)
FROM table1 t1

LEFT JOIN table2 t2
ON t1.uid = t2.uid

GROUP BY class

试试这个：

SELECT class, SUM(fee)
FROM table1 t1

LEFT JOIN table2 t2
ON t1.uid = t2.uid

GROUP BY class

试试这个

SELECT a.class, SUM(b.fee)
FROM user_classification a
INNER JOIN user_fees b
ON a.uid = b.uid
GROUP BY a.class
ORDER BY a.class ASC

试试这个

SELECT a.class, SUM(b.fee)
FROM user_classification a
INNER JOIN user_fees b
ON a.uid = b.uid
GROUP BY a.class
ORDER BY a.class ASC

---

假设第一个表tab1和第二个表tab1是tab2

select t2.class,sum(t1.fee) from tab2 t2 inner join tab1 t1 on t2.uid=t1.uid 
group by t2.class

---

假设第一个表tab1和第二个表tab1是tab2

select t2.class,sum(t1.fee) from tab2 t2 inner join tab1 t1 on t2.uid=t1.uid 
group by t2.class