add 512

fishercoder1534 · fishercoder1534 · commit 4f3cba91ceb5 · 2020-02-02T10:21:40.000-08:00
diff --git a/README.md b/README.md
@@ -896,6 +896,7 @@ _If you like this project, please leave me a star._ &#9733;
 |571|[Find Median Given Frequency of Numbers](https://leetcode.com/problems/find-median-given-frequency-of-numbers/)|[Solution](../master/database/_571.sql)  || Hard |
 |570|[Managers with at Least 5 Direct Reports](https://leetcode.com/problems/managers-with-at-least-5-direct-reports/)|[Solution](../master/database/_570.sql) || Medium |
 |569|[Median Employee Salary](https://leetcode.com/problems/median-employee-salary/)|[Solution](../master/database/_569.sql) || Hard |
+|512|[Game Play Analysis II](https://leetcode.com/problems/game-play-analysis-ii/)|[Solution](../master/database/_512.sql)|| Easy|
 |511|[Game Play Analysis I](https://leetcode.com/problems/game-play-analysis-i/)|[Solution](../master/database/_511.sql)|| Easy| 
 |262|[Trips and Users](https://leetcode.com/problems/trips-and-users/)|[Solution](../master/database/_262.sql)||Hard| Inner Join
 |197|[Rising Temperature](https://leetcode.com/problems/rising-temperature/)|[Solution](../master/database/_197.sql)|  | Easy|
diff --git a/database/_512.sql b/database/_512.sql
@@ -0,0 +1,46 @@
+--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
+(select player_id, min(event_date) from Activity group by player_id);
