Oracle 18c

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CREATE TABLE table_name (CustomerID, Amount, Dat) AS
SELECT 1, 1, DATE '2018-03-23' FROM DUAL UNION ALL
SELECT 1, 2, DATE '2020-03-24' FROM DUAL UNION ALL
SELECT 1, 3, DATE '2020-03-24' FROM DUAL UNION ALL
SELECT 1, 2, DATE '2020-03-25' FROM DUAL UNION ALL
SELECT 1, 2, DATE '2020-05-24' FROM DUAL UNION ALL
SELECT 1, 1, DATE '2020-06-15' FROM DUAL UNION ALL
SELECT 2, 7, DATE '2017-03-24' FROM DUAL UNION ALL
SELECT 2, 2, DATE '2020-03-24' FROM DUAL;
8 rows affected

ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
SELECT t.*,
       SUM(Amount) OVER (
         PARTITION BY CustomerID
         ORDER BY Dat
         RANGE BETWEEN INTERVAL '30' DAY PRECEDING AND CURRENT ROW
       ) AS ProductsIn30Days
FROM   table_name t;


CUSTOMERID
AMOUNT
DAT
PRODUCTSIN30DAYS


1
1
2018-03-23 00:00:00
1

1
2
2020-03-24 00:00:00
5

1
3
2020-03-24 00:00:00
5

1
2
2020-03-25 00:00:00
7

1
2
2020-05-24 00:00:00
2

1
1
2020-06-15 00:00:00
3

2
7
2017-03-24 00:00:00
7

2
2
2020-03-24 00:00:00
2

CUSTOMERID	AMOUNT	DAT	PRODUCTSIN30DAYS
1	1	2018-03-23 00:00:00	1
1	2	2020-03-24 00:00:00	5
1	3	2020-03-24 00:00:00	5
1	2	2020-03-25 00:00:00	7
1	2	2020-05-24 00:00:00	2
1	1	2020-06-15 00:00:00	3
2	7	2017-03-24 00:00:00	7
2	2	2020-03-24 00:00:00	2