[LeetCode][MySQL] 511. Game Play Analysis I

Easy 🔗511. Game Play Analysis I

📝문제 요약

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 find the first login date 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 | first_login |
+-----------+-------------+
| 1         | 2016-03-01  |
| 2         | 2017-06-25  |
| 3         | 2016-03-02  |
+-----------+-------------+

✏️문제 풀이

SELECT

SELECT player_id, MIN(event_date) AS first_login

• player_id : 플레이어 ID
• first_login : 첫 로그인 날짜
  • MIN(event_date) : 첫 로그인 날짜는 가장 작은 날짜이므로 MIN()을 사용하여 구함

FROM

FROM Activity

• Activity 테이블의 데이터를 가져옴

GROUP BY

GROUP BY 1

• 1번 컬럼(player_id )을 기준으로 그룹화

💯제출 코드

SELECT player_id, MIN(event_date) AS first_login
FROM Activity
GROUP BY 1