查询选修了全部课程的学生名

三张表：学生表student (Sno,Sname),  课程表course (Cno,Cname)， 选课表SC(Sno,Cno)

--选修了全部课程的学生名

select  Sname from student where Sno in 
 (select Sno from SC  group by Sno having count(*) =(select count(*) from course))

--选修了部分课程的学生名

select  Sname from student where Sno in 
 (select Sno from SC  group by Sno having count(*) <(select count(*) from course))

--没有选修课程的学生名

select  Sname from student where Sno not in
 (select Sno from SC inner join course on SC.Cno = course.Cno group by Sno

)