24 - 查询近30天活跃用户数

• 排序和分组
  
  
  
  

-- 日期相减 date_sub('2019-07-27', interval 30 day)获取新的日期
-- 日期范围 datediff('2019-07-27',activity_date)<30


-- where activity_date > date_sub('2019-07-27', interval 30 day)
-- and activity_date <= '2019-07-27'=where datediff('2019-07-27',activity_date)<30

select
    activity_date day,count(distinct user_id) active_users 
from
    Activity 
where 
    datediff('2019-07-27',activity_date)<30

GROUP BY 
    activity_date;