题解 | #找出待召回的流失用户#

考察内容：count(distinct)、max，having，datediff，order by

思路：

① 按用户分组，统计每个用户的登录天数和登录次数

② 取每个用户最后一次登录日期，表中最大日期作为当前日期，用 having 筛选用户最后一次登录日期距今30天及以上且至少登录过3天或4次的用户

③ 按要求排序输出

select 
	uid,
	count(distinct login_date) as days,
	count(id) as times
from 
	user_login_tb as a 
group by 
	uid
having (days >= 3 or times >= 4)
and datediff((select max(login_date) from user_login_tb), max(login_date))>=30
order by days desc, times desc
;