Question

512. Game Play Analysis II

中文文档

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.

# 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 $1$.

# 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;