Question

数据库包含REGISTRATION表和STUDENT表。

REGISTRATION表的列是：

CourseID, StudentID, CourseCode, Score, Year

CourseCode列包含CS-101，MS-202等课程代码（每个学生ID都注册到许多课程）。我需要找到学生参加3门以上课程的名字和身份证。

我试过了：

Select distinct 
    CourseRegistrations.S_ID, Students.FirstName
from 
    Students, CourseRegistrations
where 
    Students.StudentID = CourseRegistrations.StudentID 
group by
    CourseRegistrations.S_ID, Students.FirstName 
having 
    count(distinct CourseRegistrations.CourseCode) > 3

但这显示了文件的所有记录。

Answer 1

如果您使用Distinct

，则不需要

GROUP BY

Select CusReg.S_ID
from Students stud join CourseRegistrations CusReg
ON stud.StudentID=CusReg.StudentID 
GROUP BY CourseRegistrations.S_ID 
having count(CusReg.CourseCode)>3

不要使用旧样式联接

SOURCE

Answer 2

你应该尝试：

Select CourseRegistrations.StudentID, count(CourseRegistrations.CourseCode)
from Students, CourseRegistrations
where Students.StudentID=CourseRegistrations.StudentID 
GROUP BY CourseRegistrations.StudentID
having count(CourseRegistrations.CourseCode)>3

如何从SQL中的列中选择不同数量的值？

2 个答案: