题解 | #统计每个用户的平均刷题数#
统计每个用户的平均刷题数
https://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select u.university, q2.difficult_level, count(q1.question_id)/count(distinct(q1.device_id)) as avg_answer_cnt from user_profile as u,question_practice_detail as q1,question_detail as q2 where u.device_id = q1.device_id and q2.question_id = q1.question_id and u.university = '山东大学' group by q2.difficult_level
总结：细心点，不要漏字段，逗号
