leetcode - 512. Game Play Analysis II

난이도 : Easy

 

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 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 an SQL query to report the device that is first logged in for each player.

Return the result table in any order.

 

where절 서브쿼리를 사용한 방법

SELECT player_id
     , device_id
FROM Activity
WHERE (player_id, event_date) IN (
                                  SELECT player_id
                                       , MIN(event_date) first_log
                                  FROM Activity
                                  GROUP BY player_id
                                  )

Accepted

 

 

윈도우함수를 활용한 방법

SELECT player_id
     , device_id
FROM (
      SELECT player_id
           , device_id
           , RANK() OVER (PARTITION BY player_id ORDER BY event_date) rnk
      FROM Activity
     ) sub
WHERE rnk = 1

Accepted