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
university,difficult_level,
ROUND(COUNT(qpd.question_id)/COUNT(DISTINCT(qpd.device_id)),4) AS avg_answer_cnt
##注意精确到小数点后4位
FROM
question_practice_detail AS qpd
INNER JOIN
user_profile AS u
ON
qpd.device_id=u.device_id
INNER JOIN
question_detail AS qd
ON
qpd.question_id=qd.question_id
WHERE
u.university='山东大学'
#比上一题多一个where条件
GROUP BY
difficult_level;