Question

我有一张这样的表

+------------------------------+
| Name,Class,Value,Class_Total |
+------------------------------+
| John  ,A  ,10,        0      |
| Jake  ,A  ,22,        0      |
| Jill  ,B  ,34,        0      |
+------------------------------+

我想运行一个UPDATE查询，用每个类的总数填充Class_Total，结果将是

+------------------------------+
| Name,Class,Value,Class_Total |
+------------------------------+
| John  ,A  ,10,        32     |
| Jake  ,A  ,22,        32     |
| Jill  ,B  ,34,        34     |
+------------------------------+

目前我有这个

UPDATE  dbo.Contrived
SET Class_Total = (SELECT SUM(Value)
FROM dbo.Contrived
)

但是这会将Class_Total中所有类的总数不仅仅是行所属的类，我需要以某种方式按类对项目进行分组。我知道我可以做一个

WHERE Class ='A'

在Select中，我想自动为很多课程做。希望有意义，谢谢。

Answer 1

您可以使用简单的子查询：

UPDATE c 
SET c.Class_Total = (SELECT SUM(c2.Value)
                     FROM dbo.Contrived c2
                     WHERE c2.Class = c.Class)
FROM dbo.Contrived c

Demo-Fiddle

Answer 2

请尝试使用CTE：

;with T as(
    select *, SUM(Value) over(partition by Class) sm
    From dbo.Contrived
) update T set Class_Total=sm

如何根据列值对行更新进行分组？

2 个答案: