test/trace_processor/functions/first_non_null_partition_test.sql

CREATE TABLE TEST(id INTEGER, part TEXT, val INTEGER);

INSERT INTO TEST
VALUES
(1, 'A', 1),
(2, 'A', NULL),
(3, 'A', 3),
(4, 'B', NULL),
(5, 'B', 5),
(6, 'B', NULL),
(7, 'B', 7);

SELECT id, LAST_NON_NULL(val) OVER (PARTITION BY part ORDER BY id ASC) AS val
FROM TEST
ORDER BY id ASC;