SQL，在组中选择最大数量

Question

我有三个表，Student，Grd，Course，我想选择每门课程的最佳成绩和学生姓名。

这是我的查询，返回所有学生-名称和年级-但我只想为每门课程取得最佳成绩。

select 
    student.[name], Course.[Name] as course, max((GRD.Number)) as Grade 
from 
    GRD 
join 
    Course on Course.CO_ID = GRD.CO_ID
join 
    Student on Student.ST_ID = GRD.ST_ID
group by 
    course.[Name], Student.[Name]

我正在使用Sql服务器

Answer 1

如果您使用的是MySQL 8.0，PostgreSQL，SQL Server或Oracle，则可以使用以下方法解决您的问题。

select
    student_name,
    course,
    Grade
from
(
    select 
        s.[name] as student_name,
        c.[Name] as course,
        max(g.Number) as Grade, 
        row_number() over (partition by c.[Name] order by max(g.Number) desc) as rnk

    from GRD g
    join Course c
    on c.CO_ID = g.CO_ID

    join Student s
    on s.ST_ID = g.ST_ID

    group by 
        c.[Name],
        s.[Name]
) val
where rnk = 1