SQL 多列多表分组

Question

这是我的 tables

CREATE TABLE Course(Cno CHAR(6), Cname NVARCHAR(20) NOT NULL,PRIMARY KEY(Cno))
CREATE TABLE SC(Sno CHAR(7) NOT NULL,Cno CHAR(6) NOT NULL,Grade TINYINT,
    PRIMARY KEY(Sno, Cno),
    FOREIGN KEY(Sno) REFERENCES Student(Sno),
    FOREIGN KEY(Cno) REFERENCES Course(Cno)
)

table 课程

Cno    Cname    
------------
C001   Math
C002   CS
C003   Database

table SC

Sno    Cno    Grade
-------------------
1      C001   80
2      C002   90
2      C003   70
3      C002   60

想要...：

Cno    Cname    Number
-----------------------
C002   CS       2
C001   Math     1
C003   Database 1

此代码有效

select top 3 with ties Course.Cno, Course.Cname, count(SC.Cno) AS Number 
from Course left join SC
  on Course.Cno = SC.Cno
  group by Course.Cno, Cname, Semester
  order by count(SC.Cno) desc

但如果我使用 "goup by Course.Cno"，则无效..

为什么我必须添加 "Cname, Semester"？

我试过 mysql 成功了..但是 sql 服务器 2012 不行。

Answer 1

使用子查询获取计数：

select Cno, Cname, (select count(*) from sc where c.cno = sc.cno) as cnt
from Course as c
order by cnt

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