Fetch last available value if there is NULL - postgresql

Question

I have a table that is essentially a purchases table that has purchase prices. When a purchase is made, it is recorded at an hour. Like in the table, ABC-123 was purchased on 2022-1-20 at 12:00. I want the NULL values to show 20 as long as a new purchase price is not punched in. Same for the other id_code.
id_code
hour
purchase_price
ABC-123
2022-1-20 12:00
20
ABC-123
2022-1-20 13:00
NULL
ABC-123
2022-1-20 14:00
NULL
BCD-123
2022-1-20 12:00
35
BCD-123
2022-1-20 13:00
36
BCD-123
2022-1-20 14:00
NULL
The output table will look like this:
It will replace the NULLs with the previously available price for its particular id_code.
id_code
hour
purchase_price
ABC-123
2022-1-20 12:00
20
ABC-123
2022-1-20 13:00
20
ABC-123
2022-1-20 14:00
20
BCD-123
2022-1-20 12:00
35
BCD-123
2022-1-20 13:00
36
BCD-123
2022-1-20 14:00
36
I did find a similar question here but that seems to not work because my IDs are not incremental integers I think.

Answer 1

You can create a view with an aggregate function. Try this :
CREATE VIEW test_view AS
( SELECT id_code
, hour
, (array_agg(purchase_price) FILTER (WHERE purchase_price IS NOT NULL) OVER (PARTITION BY id_code ORDER BY hour DESC ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING))[1]
FROM test
)
Result :
id_code hour array_agg
ABC-123 2022-01-20 12:00:00 20
ABC-123 2022-01-20 13:00:00 20
ABC-123 2022-01-20 14:00:00 20
BCD-123 2022-01-20 12:00:00 35
BCD-123 2022-01-20 13:00:00 36
BCD-123 2022-01-20 14:00:00 36
see the demo in dbfiddle.