题解 48| 有点不大对劲 |个人笔记
所有用户对高难度题目的刷题数
https://www.nowcoder.com/practice/e8b66c069376405bb7524b217c890b23
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
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记录解题过程中遇到的问题、出现的错误以及掌握不牢固的知识点
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