--1
select Sname,Sage from Student where Sage<(select Sage from Student where Sno='某一学生') and Sdept='数学系'
--2
select Sname from Student where Sno in (select Sno from SC)
--3
select Sname from Student where Sno in (select Sno from SC group by Sno having count(*)=(select count(*) from Course ))
--4
题意不清楚
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024