题目：查询成绩在60分以上的学生的信息及其选课的课程号和成绩
select * from student,course where grade>=60
select student.*,cid,grade from student,sc where student.sid=sc.sid and grade>=60
select * from student,sc where student.sid=sc.sid where grade>=60
select * from student,sc where student.sid=sc.sid where student.sid=sc.sid
