Question

我有两张桌子（学生和帐户）
每个学生在学生表中都有一条记录，但在帐户表中可能有多条记录我需要在帐户表中汇总一列，按学生表中的学生代码分组

我编写了以下查询，但是当我使用GROUP BY命令时，它返回了一个错误：

select students.id,students.stcode,students.stname,account.stcode,
       sum(cast ((account.price) AS INT)) OVER () AS PriceTotal
from students 
inner join account on students.stcode=account.stcode 
group by students.stcode

错误消息：
Column 'students.id' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause。

Answer 1

您需要按不属于聚合的所有列进行分组。也就是说，如果students.stname在功能上依赖于students.stcode（即students.stcode是唯一的），您可以在students.stcode上应用max等聚合。由于account.stcode = students.stcode可以删除。我不确定over子句应该在这里做什么，所以我删除了那个，留下我们：

select students.stcode, max(students.stname) as stname
     , sum(cast (account.price AS INT)) AS PriceTotal
from students 
join account 
    on students.stcode=account.stcode 
group by students.stcode

另一种选择是在group by子句中包含students.stname：

select students.stcode, students.stname
     , sum(cast (account.price AS INT)) AS PriceTotal
from students 
join account 
    on students.stcode=account.stcode 
group by students.stcode, students.stname

如果您使用的是支持窗口功能的DBMS（您标记帖子的mysql没有），则不需要按以下组分组：

select students.stcode, students.stname
     , sum(cast (account.price AS INT)) over () AS PriceTotal
from students 
join account 
    on students.stcode=account.stcode

如何汇总连接表中的列？

1 个答案: