题解 | #所有用户对高难度题目的刷题数#
所有用户对高难度题目的刷题数
https://www.nowcoder.com/practice/e8b66c069376405bb7524b217c890b23
select a.device_id,
count(if (c.difficult_level = 'hard', 1, null)) as question_cnt
from
user_profile a
left join question_practice_detail b on a.device_id = b.device_id
left join question_detail c on b.question_id = c.question_id
group by
device_id
order by
question_cnt
