SQL 从 YTD 中计算出 MTD

Question

我尝试在 SQL MTD 中计算表的成本。

我有下表：

year	user	month	type	cost	blank
2021	a	1	type1	10	0
2021	a	2	type1	20	0
2021	a	3	type1	35	0
2022	a	1	type1	5	0
2022	a	2	type1	35	0
2021	b	1	type1	10	0
2021	b	2	type1	30	0

我现在需要的是每年、用户和类型的 MTD 成本

year	user	month	type	cost	costMTD	blank
2021	a	1	type1	10	10	0
2021	a	2	type1	20	10	0
2021	a	3	type1	35	15	0
2022	a	1	type1	5	5	0
2022	a	2	type1	35	30	0
2021	b	1	type1	10	10	0
2021	b	2	type1	30	20	0

我可以用 SQL 中的查询来做到这一点吗？

我试过这样但它不起作用：

SELECT t1.year, t1.user, t1.month, t1.type, t1.cost, 
iif(t1.month = '1', t1.cost, t1.cost- t2.cost) AS costMTD, 0 AS blank
FROM dbo.usercosts AS t1 INNER JOIN dbo.usercosts AS t2 
ON t1.year = t2.year 
AND t1.user= t2.user 
AND t1.type= t2.type 
AND t2.month = iif(t2.month = '1', '1', t1.month - 1)

Answer 1

您可以使用LAG查看上一行的费用。

select 
  year, user, month, type, cost, 
  cost - coalesce(lag(cost) over(partition by user order by year, month), 0) as costmtd, 
  0 as blank
from dbo.usercosts as
order by user, year, month;