sql计数函数加入

Question

SELECT c.cname, COUNT(e.ccode) 
FROM class c 
INNER JOIN enrolled e ON e.ccode = c.ccode 
WHERE room = 'MB100' 
AND e.ccode = < 10; 

我试图找到MB100房间里有少于10名学生的课程名称，我该怎么办？

Answer 1

你缺少group by c.cname，试试这个：

SELECT c.cname, COUNT(e.ccode) 
FROM class c 
INNER JOIN enrolled e ON e.ccode = c.ccode 
WHERE room = 'MB100' 
Group by c.cname 
Having e.ccode =< 10;