题解 | #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 count(day2.device_id) / count(day1.device_id) as avg_ret from (select distinct device_id, date from question_practice_detail) as day1 left join (select distinct device_id, date from question_practice_detail) as day2 on day1.device_id = day2.device_id and day2.date = date_add(day1.date, interval 1 day)
留存率：后一天的答题数量/ 前一天的答题数量
同一设备号，如果前一天的日期相加1等于后一天，则说明第二天前来答题了
