嵌套子查询，题目没有说清楚，后面level个数相同时用level进行排序

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