题解 48| 有点不大对劲 |个人笔记

牛客网是不是有bug,一下能通过，一下又不能。

(select device_id, '0' question_cnt
from user_profile a
where answer_cnt = 0 or answer_cnt is null)
union
(select b.device_id, count(c.difficult_level) question_cnt
from question_practice_detail b
left join question_detail c on b.question_id = c.question_id 
and c.difficult_level = 'hard'
group by b.device_id)
order by question_cnt asc