--------------------------表结构--------------------------
student(stuid,stuname,stuage,stusex) 学生表
teacher(tid,tname) 教师表
course(cid,cname,c_tid) 课程表
sc(sid,s_cid,score) 成绩表
----------------------------------------------------------
select stuid,stuname from student
where stuid in
(
select sid from sc where score<60
);
