力扣刷题学习SQL篇——1-17 查询近30天活跃用户数（日期进行区间判定）

1、题目

题目链接：https://leetcode.cn/problems/user-activity-for-the-past-30-days-i/
SQL架构

Create table If Not Exists Activity (user_id int, session_id int, activity_date date, activity_type ENUM('open_session', 'end_session', 'scroll_down', 'send_message'))
Truncate table Activity
insert into Activity (user_id, session_id, activity_date, activity_type) values ('1', '1', '2019-07-20', 'open_session')
insert into Activity (user_id, session_id, activity_date, activity_type) values ('1', 
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