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(q.question_id) / COUNT(DISTINCT u.device_id) AS avg_answer_cnt
FROM user_profile u, question_practice_detail qdl, question_detail q
WHERE qdl.question_id = q.question_id
AND u.device_id = qdl.device_id
AND university = "山东大学"
GROUP BY difficult_level
#一列中只有一组的时候不能用GROUP BY 分组
投递字节跳动等公司10个岗位 >