题解 | #试卷发布当天作答人数和平均分#

#作答试卷 得分大于过80的用户 的等级分布

#按数量降序排序（保证数量都不同--这句话真不好理解 看了答题区才明白 = =

这里是通过子查询完成的, 比较适合,思路是一步一步走的小伙伴, 三表连接也是好办法, 但是对于新手来说,一下子理清思路有点难,

select level, count(distinct uid) as level_cnt from user_info where uid in (select uid from exam_record left join examination_info using(exam_id) where score >80 and tag ='SQL') group by level order by level_cnt desc,level DESC