SQL，案例条件内的总和

Question

我正在尝试学习 sql 查询，我想解决以下问题。

假设表如下：

ID	校名	总A	总B	年级
1个	学校A	5个	5个	1个
2个	学校A	5个	5个	2个
3个	乙校	5个	5个	1个
4个	乙校	5个	5个	2个

Select schoolname
SUM(CASE WHEN (grade='1' ) THEN totalA ELSE 0 END) AS t1A,
SUM(CASE WHEN (grade='1' ) THEN totalB ELSE 0 END) AS t1B,
SUM(CASE WHEN (grade='2' ) THEN totalA ELSE 0 END) AS t2A,
SUM(CASE WHEN (grade='2' ) THEN totalB ELSE 0 END) AS t2B,

我想知道是否可以在一种情况下同时添加 totalA 和 B。

我试过

Select schoolname
CASE WHEN (grade='1' ) THEN SUM(totalA+totalB) ELSE 0 END AS Grade 1,
CASE WHEN (grade='2' ) THEN SUM(totalA+totalB) ELSE 0 END AS Grade 2,
From school
Group By schoolname

但它给我错误。

我想实现以下目标：

校名	1级	2年级
学校A	10	10
乙校	10	10

Answer 1

是的，可以在同一个表中按组查询 MySQL。

为此，您需要使用这种类型的查询：

SELECT schoolname,
    SUM(CASE WHEN (grade = 1) THEN totalA + totalB ELSE 0 END) AS grade_1,
    SUM(CASE WHEN (grade = 2) THEN totalA + totalB ELSE 0 END) AS grade_2
FROM school
GROUP BY schoolname