511. Game Play Analysis I

Giới thiệu bài toán

Table: Activity

(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.

Yêu cầu

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.

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