题解 | #某乎问答最大连续回答问题天数大于等于3天的用户及其对应等级#

1. 经典连续登录问题解决
2. 对于俩表连接，为answer表拼接level标签列
3. 进行窗口函数的计算，计算出每位用户登录日期的排名
4. 根据用户id，登录日期与排名的差值分组计数(只要是连续登录，登录日期与排名的差值为同一天)

select b.author_id,b.author_level,count(*) days_cnt
FROM(
    select a.author_id,a.author_level,a.answer_date,row_number() over(partition by a.author_id order by a.answer_date) rk
from(
    select distinct answer_date,author_id,author_level
    from author_tb
    join answer_tb using(author_id)
) a
    )b
group by  b.author_id,(b.answer_date-rk)
having days_cnt>=3