Oracle 18c

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CREATE TABLE MAKE_IT_WORK
    (
      PRODUCT_KEY    NUMBER,
      WEEK           NUMBER,
      OPENING_STOCK  NUMBER,
      INTAKE         NUMBER,
      SALES          NUMBER,
      CLOSING_STOCK  NUMBER,
      FORWARD_COVER  NUMBER
    );
Insert into MAKE_IT_WORK  (PRODUCT_KEY, WEEK)
 Values   (1, 1);
1 rows affected

Insert into MAKE_IT_WORK   (PRODUCT_KEY, WEEK, INTAKE, SALES)
 Values   (1, 2, 1000, 80);
1 rows affected

Insert into MAKE_IT_WORK   (PRODUCT_KEY, WEEK, SALES)
 Values   (1, 3, 70);
1 rows affected

Insert into MAKE_IT_WORK  (PRODUCT_KEY, WEEK, SALES)
 Values (1, 4, 90);
1 rows affected

Insert into MAKE_IT_WORK (PRODUCT_KEY, WEEK, SALES)
 Values (2, 1, 0);
1 rows affected

Insert into MAKE_IT_WORK (PRODUCT_KEY, WEEK, INTAKE, SALES)
 Values (2, 2, 6000, 500);
1 rows affected

Insert into MAKE_IT_WORK (PRODUCT_KEY, WEEK, SALES)
 Values (2, 3, 70);
1 rows affected

Insert into MAKE_IT_WORK (PRODUCT_KEY, WEEK, SALES)
 Values (2, 4, 350);
1 rows affected

select product_key, week, opening_stock, intake, sales,
  coalesce(opening_stock, 0)
    + sum(intake) over(partition by product_key order by week)
    - sum(sales) over(partition by product_key order by week) 
    as closing_stock
from make_it_work
order by product_key, week;


PRODUCT_KEY
WEEK
OPENING_STOCK
INTAKE
SALES
CLOSING_STOCK


1
1
null
null
null
null

1
2
null
1000
80
920

1
3
null
null
70
850

1
4
null
null
90
760

2
1
null
null
0
null

2
2
null
6000
500
5500

2
3
null
null
70
5430

2
4
null
null
350
5080

PRODUCT_KEY	WEEK	OPENING_STOCK	INTAKE	SALES	CLOSING_STOCK
1	1	null	null	null	null
1	2	null	1000	80	920
1	3	null	null	70	850
1	4	null	null	90	760
2	1	null	null	0	null
2	2	null	6000	500	5500
2	3	null	null	70	5430
2	4	null	null	350	5080