题解 | #作答试卷得分大于过80的人的用户等级分布#

# 统计作答 SQL 类别的试卷的分大于过 80 的用户等级分布，数量降序排序
# 思路：
# 1. 先筛选出 SQL 类别的试卷
# 2. 查询作答记录表，筛选出用户
# 3. 查询用户表获取用户等级

select level, count(distinct ui.uid) as level_cnt
from exam_record er inner join user_info ui on er.uid = ui.uid 
where er.exam_id in(
    select exam_id 
    from examination_info
    where tag = 'SQL') and submit_time is not null and score > 80
group by level
order by level_cnt desc, level desc