【MySQL】MIN()、MAX()比较日期大小

思路：注意题目的两个关键词，每位玩家，所以用GROUP BY

第一次的日期，所以用MIN(DATE)

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

这种很方便，不过窗口函数会快点

SELECT  s.player_id,s.event_date AS `first_login`
FROM    (SELECT  a.player_id,a.event_date,ROW_NUMBER() OVER (PARTITION BY    a.player_idORDER BY a.event_date) AS nFROM    Activity AS a) AS s
WHERE   s.n = 1;

或者这么写

SELECT  DISTINCT a.player_id,FIRST_VALUE(a.event_date) OVER (PARTITION BYa.player_idORDER BYa.event_date) AS first_login
FROMActivity AS a;