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 university, qd.difficult_level difficult_level, ROUND(COUNT(qpd.question_id) / COUNT(DISTINCT up.device_id), 4) avg_answer_cnt FROM user_profile up, question_practice_detail qpd, question_detail qd WHERE up.university = '山东大学'AND up.device_id = qpd.device_id AND qpd.question_id = qd.question_id GROUP BY qd.difficult_level;
