奔跑在路上you的博客

select students.class_id,students.score,classes.name from students right join classes on students.id=classes.id order by students.score 右连接 返回右表的行。select score from students where score > (select avg(score) from students) AVG（）指定列下的平均值 求分数列下大于分数的平均值的行。