Question

我有一个场景，一所大学的学生就某一主题进行研究。每个主题都有一些价值（标记）。学生可以对多个科目进行研究。

我有以下表格层次结构：

student (s)
---------------
student_id  subject_id

1           2
2           1
2           3
3           1
3           3
4           2
4           3
.....


research_subjects (r)
-----------------------------
id      value

1       5
2       10
3       20
4       40
....

现在，我正在通过此查询获取学生记录及其总研究价值：

select student_id, sum(r.value) as total from student s inner join research_subjects r on s.subject_id=r.id group by student_id

这给出了如下结果：

student_id  total

1           10
2           25
3           25
4           30

如您所见，结果按 student_id 分组。但我想要的是按总值对结果进行分组。所以我想在输出中删除 total 的重复行。（即只有1条记录，总数= 25）。

我尝试在查询中使用 group by total （而不是 group by student_id ），但它会出错。是否有任何其他方法可以按照包含＆＃39; sum＆＃39;的列对结果进行分组？值？

Answer 1

试试这个：

select count(student_id), total
  from ( 
    select student_id, sum(r.value) as total 
     from student s 
     inner 
     join research r on s.subject_id=r.id group by student_id
     ) s2
 group by total

Answer 2

试试这个：

select Count(student_id) as students, total
from
(
    select student_id, sum(r.value) as total 
    from student s inner join research r on s.subject_id=r.id 
    group by student_id
) s
group by total

或者这个：

 select Min(student_id) as student_id, total
    from
    (
        select student_id, sum(r.value) as total 
        from student s inner join research r on s.subject_id=r.id 
        group by student_id
    ) s
    group by total

mysql group by on sum column

2 个答案: