mysql多表查询连接问题,

Question

题目：查询平均成绩在80分及以上的所有学生的学号及平均成绩并按平均成绩降序排列。

SELECT s1.sno FROM student s1,class c1,timetable t,course c2,score s2 WHERE s1.classid = c1.classid AND c1.classid = t.classid AND t.courseid = c2.courseidAND c2.courseid = s2.courseid; 写到这里一脸懵逼,怎么做啊？

Answer 1

select sno,avg_score
from (select avg(score) avg_score, sno from score group by sno)
where avg_score > 80 order by avg_score desc;