Postgres 14

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CREATE TABLE test(id_code text, hour timestamp, purchase_price integer) ;

INSERT INTO test VALUES 
('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);
6 rows affected

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
)
SELECT *
  FROM test_view
 ORDER BY id_code, hour


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

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