Oracle 23c

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CREATE TABLE sale(week int, sales int);
INSERT ALL 
    INTO sale (week, sales) VALUES (1, 10)
    INTO sale (week, sales) VALUES (1, 15)
    INTO sale (week, sales) VALUES (3, 5)
    INTO sale (week, sales) VALUES (3, 10)
    INTO sale (week, sales) VALUES (4, 10)
    INTO sale (week, sales) VALUES (4, 20)
    INTO sale (week, sales) VALUES (5, 5)
    INTO sale (week, sales) VALUES (5, 10)
    INTO sale (week, sales) VALUES (9, 15)
    INTO sale (week, sales) VALUES (9, 10)
SELECT * FROM dual;
10 rows affected

WITH rcte(week, maxval) AS (
    SELECT MIN(week), MAX(week) - 2
    FROM sale
    UNION ALL
    SELECT week + 1, maxval
    FROM rcte
    WHERE week + 1 <= maxval
), cte AS (
    SELECT week, sales
    FROM sale
    UNION ALL
    SELECT week, 0
    FROM rcte
)
SELECT
    CONCAT(week, '-', week + 2) AS period,
    SUM(SUM(sales)) OVER (ORDER BY week ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING) AS total,
    week AS debug_curr_week,
    SUM(sales) AS debug_week_sales
FROM cte
GROUP BY week
ORDER BY week


PERIOD
TOTAL
DEBUG_CURR_WEEK
DEBUG_WEEK_SALES


1-3
40
1
25

2-4
45
2
0

3-5
60
3
15

4-6
45
4
30

5-7
15
5
15

6-8
25
6
0

7-9
25
7
0

9-11
25
9
25

PERIOD	TOTAL	DEBUG_CURR_WEEK	DEBUG_WEEK_SALES
1-3	40	1	25
2-4	45	2	0
3-5	60	3	15
4-6	45	4	30
5-7	15	5	15
6-8	25	6	0
7-9	25	7	0
9-11	25	9	25