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 | +-----------+-----------+
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.
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
# 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
);# 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;