要求：查询物理成绩最高的学生，表：stu,表：cource, 表：score

SELECT d.user,MAX(d.score) FROM (SELECT a.user,b.c_name,c.score FROM stu a,course b,score c WHERE b.id=c.`c_id` AND c.`u_id`=a.`id`)  d WHERE d.c_name='物理';

1.student

2.course

3.score     u_id--->用户ID，c_id-->课程的ID

4.stu