Ниже для BigQuery Standard SQL
#standardSQL
SELECT date, value,
SUM(value) OVER(ORDER BY date DESC ROWS BETWEEN CURRENT ROW AND 5 FOLLOWING) Value_A,
IFNULL(SUM(value) OVER(ORDER BY date DESC ROWS BETWEEN 6 FOLLOWING AND UNBOUNDED FOLLOWING), 0) Value_B
FROM `project.dataset.table`
-- ORDER BY date DESC
Если применить к образцу данных из вашего вопроса, как в примере ниже
#standardSQL
WITH `project.dataset.table` AS (
SELECT 20 date, 10 value UNION ALL
SELECT 19, 10 UNION ALL
SELECT 18, 10 UNION ALL
SELECT 17, 10 UNION ALL
SELECT 16, 10 UNION ALL
SELECT 15, 10 UNION ALL
SELECT 14, 10 UNION ALL
SELECT 13, 10 UNION ALL
SELECT 12, 10 UNION ALL
SELECT 11, 10 UNION ALL
SELECT 10, 10 UNION ALL
SELECT 9, 10 UNION ALL
SELECT 8, 10 UNION ALL
SELECT 7, 10 UNION ALL
SELECT 6, 10 UNION ALL
SELECT 5, 10 UNION ALL
SELECT 4, 10 UNION ALL
SELECT 3, 10 UNION ALL
SELECT 2, 10 UNION ALL
SELECT 1, 10
)
SELECT date, value,
SUM(value) OVER(ORDER BY date DESC ROWS BETWEEN CURRENT ROW AND 5 FOLLOWING) Value_A,
IFNULL(SUM(value) OVER(ORDER BY date DESC ROWS BETWEEN 6 FOLLOWING AND UNBOUNDED FOLLOWING), 0) Value_B
FROM `project.dataset.table`
ORDER BY date DESC
результат равен
Row date value Value_A Value_B
1 20 10 60 140
2 19 10 60 130
3 18 10 60 120
4 17 10 60 110
5 16 10 60 100
6 15 10 60 90
7 14 10 60 80
8 13 10 60 70
9 12 10 60 60
10 11 10 60 50
11 10 10 60 40
12 9 10 60 30
13 8 10 60 20
14 7 10 60 10
15 6 10 60 0
16 5 10 50 0
17 4 10 40 0
18 3 10 30 0
19 2 10 20 0
20 1 10 10 0