sql - Cumulative Sum of last 12 months -

i trying make cumulative sum of last 12 months so, example on 201702 should show sum of 201603 201702.

right have following query:

select date,        product,        sum(sales) on (partition product order date) cumulative  sales 

the data this:

   date	product	sales	sales acum  201601	1	7648	7648  201602	1	5538	13186  201603	1	7659	20845  201604	1	6943	27788  201605	1	7604	35392  201606	1	4398	39790  201607	1	3261	43051  201608	1	3040	46091  201609	1	5637	51728  201610	1	5520	57248  201611	1	8554	65802  201612	1	4794	70596  201701	1	6704	69652  201702	1	2234	66348  201703	1	4093	62782  201704	1	4171	60010  201705	1	6741	59147  201706	1	2902	57651  201601	2	582	582  201602	2	2393	100416  201603	2	4614	105030  201604	2	2611	107641  201605	2	6891	114532  201606	2	4409	118941  201607	2	5454	124395  201608	2	7927	132322  201609	2	6797	139119  201610	2	6740	145859  201611	2	8077	153936  201612	2	5143	159079  201701	2	6383	67439  201702	2	1593	66639  201703	2	5352	67377  201704	2	4065	68831  201705	2	7434	69374  201706	2	2332	67297

if want information sales during last year, appropriate condition in where clause should present. oracle can use following query:

select date,   product,   sum(sales) on (partition product order date) cumulative  sales date >= add_months(sysdate, -12)