eg：统计1-12月的累积销量，即1月为1月份的值，2月为1.2月份值的和，3月为123月份的和，12月为1-12月份值的和
SELECT
month,SUM(amount) month_amount,
SUM( SUM(amount)) OVER (ORDER BY month ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS cumulative_amount
FROM table_name
GROUP BY month
ORDER BY month;
其中： SUM( SUM(amount)) 内部的SUM(amount)为需要累加的值，在上述可以换为 month_amount ORDER BY month 按月份对查询读取的记录进行排序，就是窗口范围内的排序
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW 定义起点和终点，UNBOUNDED PRECEDING 为起点，表明从第一行开始, CURRENT ROW为默认值，就是这一句等价于：
ROWS UNBOUNDED PRECEDING
PRECEDING：在前 N 行的意思。
FOLLOWING：在后 N 行的意思。
计算前3个月之间的和
SUM( SUM(amount)) OVER (ORDER BY month ROWS BETWEEN 3 PRECEDING AND CURRENT ROW) AS cumulative_amount
或者
SUM( SUM(amount)) OVER (ORDER BY month 3 PRECENDING) AS cumulative_amount
前后一个月之间的和
SUM( SUM(amount)) OVER (ORDER BY month ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING) AS cumulative_amount
统计7.23到7.26的累计和，实现结果为：
2018-07-23 10527150773 10527150773
2018-07-24 11799445150 22326595923
2018-07-25 11238537810 33565133733
2018-07-26 10917352755 44482486488
select datemion,sum(loan_amount),sum(sum(loan_amount)) OVER (ORDER BY datemion ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
from(
select datemion,strdeptcode,loan_amount,b.busiarea_code
from a
inner b
on a.strdeptcode = b.dept_code
where a.datemion between '2018-07-23' and '2018-07-26') a
group by datemion
如果按照每个月内去累加，添加分区字段即可，表示按月分区，每个月内进行累加求和，从当月1号到月末：
select datemion,sum(loan_amount),sum(sum(loan_amount)) OVER (distribute by date_format(datemion,'yyyy-MM') sort BY datemion ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
from(
select datemion,strdeptcode,loan_amount,b.busiarea_code
from app.app_total_busioverview_aggre a
inner join dim.dim_department_v b
on a.strdeptcode = b.dept_code
where a.datemion between '2018-07-23' and '2018-09-26') a
group by datemion
order by datemion;