题目链接：​​点击打开链接​​

题目大意：略。

解题思路：略。

AC 代码

SELECT IFNULL(ROUND(COUNT(DISTINCT session_id)/COUNT(DISTINCT user_id), 2), 0.0) average_sessions_per_user
FROM Activity
WHERE DATEDIFF('2019-07-27', activity_date) < 30