How can I partition by group that falls within a time range? - sql

Question

I have the following table showing when customers bought a certain product. The data I have is CustomerID, Amount, Dat. I am trying to create the column ProductsIn30Days, which represents how many products a customer bought in the range Dat-30 days inclusive the current day.
For example, ProductsIn30Days for CustomerID 1 on Dat 25.3.2020 is 7, since the customer bought 2 products on 25.3.2020 and 5 more products on 24.3.2020, which falls within 30 days before 25.3.2020.
CustomerID
Amount
Dat
ProductsIn30Days
1
1
23.3.2018
1
1
2
24.3.2020
2
1
3
24.3.2020
5
1
2
25.3.2020
7
1
2
24.5.2020
2
1
1
15.6.2020
3
2
7
24.3.2017
7
2
2
24.3.2020
2
I tried something like this with no success, since the partition only works on a single date rather than on a range like I would need:
select CustomerID, Amount, Dat,
sum(Amount) over (partition by CustomerID, Dat-30)
from table
Thank you for help.

Answer 1

You can use an analytic SUM function with a range window:
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;
Which, for the sample data:
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;
Outputs:
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
Note: If you have values on the same date then they will be tied in the order and always aggregated together (i.e. rows 2 & 3). If you want them to be aggregated separately then you need to order by something else to break the ties but that would not work with a RANGE window.
db<>fiddle here