512:游戏玩法分析II

SQL架构

Create table If Not Exists Activity_512 (player_id int, device_id int, event_date date, games_played int);
 Truncate table Activity_512;
 insert into Activity_512 (player_id, device_id, event_date, games_played) values ('1', '2', '2016-03-01', '5');
 insert into Activity_512 (player_id, device_id, event_date, games_played) values ('1', '2', '2016-05-02', '6');
 insert into Activity_512 (player_id, device_id, event_date, games_played) values ('1', '3', '2017-06-25', '1');
 insert into Activity_512 (player_id, device_id, event_date, games_played) values ('3', '1', '2016-03-02', '0');
 insert into Activity_512 (player_id, device_id, event_date, games_played) values ('3', '4', '2018-07-03', '5');

Table: Activity
 +--------------+---------+
 | Column Name  | Type    |
 +--------------+---------+
 | player_id    | int     |
 | device_id    | int     |
 | event_date   | date    |
 | games_played | int     |
 +--------------+---------+
 (player_id, event_date) 是这个表的两个主键
 这个表显示的是某些游戏玩家的游戏活动情况
 每一行是在某天使用某个设备登出之前登录并玩多个游戏（可能为0）的玩家的记录
 ​
 请编写一个 SQL 查询，描述每一个玩家首次登陆的设备名称
 ​
 查询结果格式在以下示例中：
 ​
Activity table:
 +-----------+-----------+------------+--------------+
 | player_id | device_id | event_date | games_played |
 +-----------+-----------+------------+--------------+
 | 1         | 2         | 2016-03-01 | 5            |
 | 1         | 2         | 2016-05-02 | 6            |
 | 2         | 3         | 2017-06-25 | 1            |
 | 3         | 1         | 2016-03-02 | 0            |
 | 3         | 4         | 2018-07-03 | 5            |
 +-----------+-----------+------------+--------------+
 ​
Result table:
 +-----------+-----------+
 | player_id | device_id |
 +-----------+-----------+
 | 1         | 2         |
 | 2         | 3         |
 | 3         | 1         |
 +-----------+-----------+
 
解题:

SELECT
     player_id, 
     device_id
 FROM
     (SELECT
         player_id,
         device_id,
         ROW_NUMBER() OVER(PARTITION BY player_id ORDER BY event_date) AS rn
     FROM
         Activity_512) AS a
 WHERE 
     rn = 1;