512. Game Play Analysis II

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 (combination of columns with unique values) of this table.
This table shows the activity of players of some games.
Each row is a record of a player who logged in and played a number of games (possibly 0) before logging out on someday using some device.

 

Write a solution to report the device that is first logged in for each player.

Return the result table in any order.

The result format is in the following example.

 

Example 1:

Input: 
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            |
+-----------+-----------+------------+--------------+
Output: 
+-----------+-----------+
| player_id | device_id |
+-----------+-----------+
| 1         | 2         |
| 2         | 3         |
| 3         | 1         |
+-----------+-----------+

Solutions

Solution 1: Subquery

We can use GROUP BY and MIN functions to find the first login date for each player, and then use a subquery with a composite key to find the first login device for each player.

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# 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) AS event_date
        FROM Activity
        GROUP BY 1
    );

Solution 2: Window Function

We can use the window function rank(), which assigns a rank to each login date for each player, and then select the rows with a rank of $1$.

SQL Code
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# Write your MySQL query statement below
WITH
    T AS (
        SELECT
            *,
            RANK() OVER (
                PARTITION BY player_id
                ORDER BY event_date
            ) AS rk
        FROM Activity
    )
SELECT player_id, device_id
FROM T
WHERE rk = 1;