https://blog.csdn.net/weixin_43332500/article/details/105033468
1、語法：
sum(字段1 ) over (partition by 字段2 order by 字段3 rows between unbounded preceding and current row) as 新字段名
2、功能：
實現組內累加
3. 例子
select name,mon,tota_amount,
sum(tota_amount) over(partition by name order by mon rows between unbounded preceding and current row) as account
from
(select name,mon,sum(amount) as tota_amount
from sheet1
group by name,mon) as a
select name,mon,tota_amount,
sum(tota_amount) over(partition by name order by mon rows between unbounded preceding and current row) as account
from
(select name,mon,sum(amount) as tota_amount
from sheet1
group by name,mon) as a
4、函數說明
sum(tota_amount)的求和是針對后面over()窗口的求和，
over中partition by name order by mon 針對name這一組按照月份排序，
rows between unbounded preceding and current row 限定了行是按照在當前行不限定的往前處理，通俗就是處理當前以及之前的所有行的sum，即3月時sum(amount)求的時1、2、3月的和，2月時sum(amount)求的是1、2月的和。unbounded意思無限的 preceding在之前的，current row當前行。