1369.(Hard)获取最近第二次的活动

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：

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  |
+------------+--------------+-------------+-------------+

Result 表:
+------------+--------------+-------------+-------------+
| username   | activity     | startDate   | endDate     |
+------------+--------------+-------------+-------------+
| Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
| Bob        | Travel       | 2020-02-11  | 2020-02-18  |
+------------+--------------+-------------+-------------+

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

来源：力扣（LeetCode）

链接：https://leetcode-cn.com/problems/get-the-second-most-recent-activity

著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

Solution

select username,activity,startDate,endDate
from(
    select *,
        rank() over (partition by username order by startDate desc) dt_rank,
        count(*) over (partition by username) cnt 
    from UserActivity
) a
where dt_rank = 2 or cnt = 1;

Table Schema

Create table If Not Exists UserActivity (username varchar(30), activity varchar(30), startDate date, endDate date);
Truncate table UserActivity;
insert into UserActivity (username, activity, startDate, endDate) values ('Alice', 'Travel', '2020-02-12', '2020-02-20');
insert into UserActivity (username, activity, startDate, endDate) values ('Alice', 'Dancing', '2020-02-21', '2020-02-23');
insert into UserActivity (username, activity, startDate, endDate) values ('Alice', 'Travel', '2020-02-24', '2020-02-28');
insert into UserActivity (username, activity, startDate, endDate) values ('Bob', 'Travel', '2020-02-11', '2020-02-18');