sql实现查询学习了所有课程的学⽣信息
select Sname from student
where Sno IN
(select Sno from SC
group by Sno //根据Sno分组，统计每个学⽣选修了⼏门课程。如果等于course的总数，就是我们要的Sno      having count(*) = (select count(*)from course ))    //统计course中共有⼏门课程
--⽤⼀个简单逻辑
SELECT SNo
sql容易学吗FROM CourseSelection
GROUP BY SNo
HAVING COUNT(*) = (SELECT COUNT(*)FROM Course) -- 选课数 = 课程总数