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
http://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
SELECT up.university as university, qd.difficult_level as difficult_level, COUNT(qpd.question_id)/COUNT(distinct qpd.device_id) as avg_answer_cnt FROM question_practice_detail as qpd INNER JOIN user_profile as up ON up.device_id = qpd.device_id AND up.university='山东大学' INNER JOIN question_detail as qd ON qd.question_id = qpd.question_id GROUP BY qd.difficult_level;