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Formatted question description: https://leetcode.ca/all/512.html
512. Game Play Analysis II
Level
Easy
Description
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 |
+-----------+-----------+
Solution
Use nested select statement. In the inner select statement, select the minimum event_date for each player_id. In the outer select statement, select the player_id and the device_id using the minimum event_date as the condition.
# 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);