分开计算 | #计算用户的平均次日留存率#
计算用户的平均次日留存率
https://www.nowcoder.com/practice/126083961ae0415fbde061d7ebbde453
select (select count(distinct a.device_id, a.date) from question_practice_detail a join question_practice_detail b on a.device_id = b.device_id and datediff(b.date, a.date) = 1) / (select count(distinct device_id, date) from question_practice_detail) avg_ret
分两个表计算用户id、日期去重后的用户数，满足次日留存即日期数相差1，示例结果应为3/10=0.3。
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