refactor 512

Author: fishercoder1534

database/_512.sql

@@ -1,45 +1,3 @@
---512. Game Play Analysis II
---
---Table: Activity
---
---+--------------+---------+
---| Column Name  | Type    |
---+--------------+---------+
---| player_id    | int     |
---| device_id    | int     |
---| event_date   | date    |
---| games_played | int     |
---+--------------+---------+
---(player_id, event_date) is the primary key of this table.
---This table shows the activity of players of some game.
---Each row is a record of a player who logged in and played a number of games (possibly 0) before logging out on some day using some device.
---
---
---Write a SQL query that reports the device that is first logged in for each player.
---
---The query result format is in the following example:
---
---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         |
---+-----------+-----------+
-
---# Write your MySQL query statement below
 select player_id, device_id from Activity where
 (player_id, event_date)
 in