无处不在的partition by

之前看到partition by在排名函数用过，也在sum函数里用过，这次又在case when里套用，学习了：

select company_id,employee_id,employee_name,case when max(salary) over(partition by company_id)<1000 then salary when max(salary) over(partition by company_id) between 1000 and 10000 then round(0.76*salary,0)else round(0.51*salary,0) end as salary 
from Salaries
order by company_id,employee_id

 534. 游戏玩法分析 III - 力扣（LeetCode）

编写一个 SQL 查询，同时报告每组玩家和日期，以及玩家到目前为止玩了多少游戏。也就是说，在此日期之前玩家所玩的游戏总数。

 partition by有兼顾前后的味道，不管是排名还是下面的累加。

selectplayer_id,event_date,sum(games_played) over(partition by player_id order by event_date) as games_played_so_far
fromactivity

select * from
activity a1,activity a2
where
a1.player_id=a2.player_id
and
a1.event_date>=a2.event_date

select a1.player_id,a1.event_date,sum(a2.games_played) games_played_so_far
from
activity a1,activity a2
where
a1.player_id=a2.player_id
and
a1.event_date>=a2.event_date
group by a1.player_id,a1.event_date
order by player_id,event_date