# 查询所有有过作答SQL类别试卷得分大于80记录的用户等级分布
select level, count(distinct ui.uid) level_cnt
from user_info ui
join exam_record er
on ui.uid=er.uid
join examination_info ei
on er.exam_id=ei.exam_id
where tag = 'SQL'
and score>80
group by level
order by level_cnt desc, level desc;