sql练习-- 计算用户的平均次日留存率

描述

题目：现在运营想要查看用户在某天刷题后第二天还会再来刷题的平均概率。请你取出相应数据。

 

示例：question_practice_detail

id	device_id	quest_id	result	date
1	2138	111	wrong	2021-05-03
2	3214	112	wrong	2021-05-09
3	3214	113	wrong	2021-06-15
4	6543	111	right	2021-08-13
5	2315	115	right	2021-08-13
6	2315	116	right	2021-08-14
7	2315	117	wrong	2021-08-15
……

根据示例，你的查询应返回以下结果：

avg_ret

0.3000

select count(date2)/count(date1) as avg_ret
from(
    select 
        distinct q.device_id,
        q.date date1,
        u_d.date date2
        from question_practice_detail as q 
        left join(
            select distinct device_id,date
            from question_practice_detail
        )as u_d
        on q.device_id = u_d.device_id
        and date_add(q.date,interval 1 day) = u_d.date
)lat