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 university,difficult_level, count(qpd.device_id)/count(DISTINCT qpd.device_id) as avg_answer_cnt FROM user_profile as up LEFT JOIN question_practice_detail as qpd On up.device_id=qpd.device_id LEFT JOIN question_detail as qd ON qpd.question_id=qd.question_id Group by difficult_level,university HAVING university='山东大学'
