1369. 获取最近第二次的活动

SQL架构

表: UserActivity

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| username      | varchar |
| activity      | varchar |
| startDate     | Date    |
| endDate       | Date    |
+---------------+---------+
该表不包含主键
该表包含每个用户在一段时间内进行的活动的信息
名为 username 的用户在 startDate 到 endDate 日内有一次活动

写一条SQL查询展示每一位用户 最近第二次 的活动

如果用户仅有一次活动，返回该活动

一个用户不能同时进行超过一项活动，以 任意 顺序返回结果

下面是查询结果格式的例子。

示例 1：

输入：
UserActivity 表:
+------------+--------------+-------------+-------------+
| username   | activity     | startDate   | endDate     |
+------------+--------------+-------------+-------------+
| Alice      | Travel       | 2020-02-12  | 2020-02-20  |
| Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
| Alice      | Travel       | 2020-02-24  | 2020-02-28  |
| Bob        | Travel       | 2020-02-11  | 2020-02-18  |
+------------+--------------+-------------+-------------+
输出：
+------------+--------------+-------------+-------------+
| username   | activity     | startDate   | endDate     |
+------------+--------------+-------------+-------------+
| Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
| Bob        | Travel       | 2020-02-11  | 2020-02-18  |
+------------+--------------+-------------+-------------+
解释：
Alice 最近一次的活动是从 2020-02-24 到 2020-02-28 的旅行, 在此之前的 2020-02-21 到 2020-02-23 她进行了舞蹈
Bob 只有一条记录，我们就取这条记录

with e as (select
username,activity, row_number() over(partition by username order by startDate desc) r,startDate,endDate
from
UserActivity)
 
select username,activity,startDate,endDate from e where r =2
union all
select username,activity,startDate,endDate from e where r = 1 and username not in (select username from e where r =2)

with e as (select
username,activity, row_number() over(partition by username order by startDate desc) r,startDate,endDate
from
UserActivity)  # 封装成 虚拟表 减少 重复代码的书写
 
select username,activity,startDate,endDate from e where r =2  # 选出 第二次 的活动
union all
select username,activity,startDate,endDate from e where r = 1 and username not in (select username from e where r =2) 
# 选出 只有 一次 的 活动

开两个窗:

SELECT u1.username,u1.activity,u1.startDate,u1.endDate
from(
SELECT *,
    rank() over(partition by username order by startDate desc ) as 'rank1',
    COUNT(*)over(partition by username  ) as 'count1'
FROM UserActivity) as u1
WHERE rank1 = 2 
or count1 =1