题解 | 计算用户的平均次日留存率

select 
count(t2.device_id)/count(t1.device_id) as avg_ret
from (select distinct device_id,date 
             from question_practice_detail  )t1
left join
      (select distinct device_id,date 
             from question_practice_detail  )t2
on t1.device_id = t2.device_id and t2.date=date_add(t1.date,interval 1 day);

t1表为原表

左连接

t2.date=t1.date+1(t2.date=date_add(t1.date,interval 1 day))

对两表的device_id进行distinct去重

留存率count(t2.device_id)/count(t1.device_id)