学生表student
老师表teacher
课程表course
分数表test
1.数学比语文成绩高的所有学生姓名
select name from (select a.sid from (select * from test where cid=1) a ,(select * from test where cid=2) b where a.sid=b.sid and a.score>b.score) c left join (select sid,name from student) d on c.sid=d.sid
原文：http://www.cnblogs.com/fj0716/p/6246373.html