text: 
  /*---------------------------------------------------------------------
  Exercise 511
  
  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 game.
  Each row is a record of a player who logged in and played a number of games (possibly 0) before logging out on some day using some device.
   
  Write an SQL query that reports the first login date for each player.
  
  The query result format is in the following example:
  
  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            |
  +-----------+-----------+------------+--------------+
  
  Result table:
  +-----------+-------------+
  | player_id | first_login |
  +-----------+-------------+
  | 1         | 2016-03-01  |
  | 2         | 2017-06-25  |
  | 3         | 2016-03-02  |
  +-----------+-------------+
  
  */---------------------------------------------------------------------
  USE QuestionBank
  GO
  
  DROP TABLE IF EXISTS dbo.Activity
  GO
  
  CREATE TABLE dbo.Activity (
  	player_id    INT  NOT NULL
    , device_id    INT  NOT NULL
    , event_date   DATE NOT NULL
    , games_played INT  NOT NULL
    CONSTRAINT PK_dbo_Activity_player_id_event_date PRIMARY KEY (player_id, event_date)
  )
  
  INSERT INTO dbo.Activity (player_id, device_id, event_date, games_played) 
  VALUES (1, 2, '2016-03-01', 5)
       , (1, 2, '2016-05-02', 6)
  	 , (2, 3, '2016-06-25', 1)
  	 , (3, 1, '2016-03-02', 0)
  	 , (3, 4, '2016-07-03', 5)
  
  SELECT * FROM Activity
  
  --1.
  SELECT player_id
       , MIN(event_date) 'first_login'
  FROM Activity
  GROUP BY player_id