step1:将2021年6月份所有的用户根据user_id进行分组并按登录时间升序排序后进行编号，编号记为rn；

step2:按照user_id及login_date-rn进行分组，过滤连续登录天数大于3天的用户；

step3:统计满足要求的所有的用户数。

row_number() over(partition by col1 order by col2)的含义为对先按col1进行分组，再按col2进行排序的结果依次进行编号。

SELECT count(*) AS num

FROM(

SELECT user_id, count(*) as days_count

FROM (

SELECT *

​ ,row_number() over (partition by user_id order by login_date asc) as rn

FROM logintb WHERE DATE_FORMAT(login_date, '%Y-%m')='2021-06') t

group by user_id,DATE_ADD(login_date,interval - rn day)

HAVING days_count >= 3

) t1;