oj-sql

题目

1141. 查询近30天活跃用户数

思路

1. 先筛选，再分组，再计数；

solution

where groupby count

select activity_date as day, count(distinct user_id) as active_users
from Activity
where activity_date between '2019-06-28' and '2019-07-27'
group by activity_date
;