The Report(连接查询)

给出学生表(id, name, marks)和等级表(grade, min_mark, max_mark)

输出要求：

1.等级降序输出 

2.等级小于8的用null替代名字

3.等级(大于等于8)相等，按名字升序;等级小于8相等时，按分数升序排列

select (case g.grade >= 8 when true then s.name else null end), g.grade, s.marks from students  as s inner join grades as g on s.marks between min_mark and max_mark order by g.grade desc, s.name, s.marks;