Leetcode_534_游戏玩法分析3_SQL

select a1.player_id, a1.event_date, sum(a2.games_played) as games_played_so_far
from activity as a1 join activity as a2 on a1.player_id = a2.player_id
where a1.event_date >= a2.event_date
group by a1.player_id, a1.event_date

select
	player_id,
	event_date,
	sum(games_played)
	 over(partition by player_id order by event_date) as games_played_so_far
from activity;

over也可以用于sum函数后, 按序累加