LeetCode MySQL-511. Game Play Analysis I

    AllenLi
    LeetCode MySQL

    Write an SQL query to report the first login date for each player.
    Return the result table in any order.

    寫一個 SQL Query來報告每個玩家的首次登入日期。
可任意排序結果。

    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.

    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  |
+-----------+-------------+

    Solution:
    1. 選擇標題 player_id。
    2. 選擇標題 first_login 為最小的 event_date。
    3. 以 player_id 為群組。

    Code1:

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

    newActivitydate

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