Example of hypotetical FIRST, SECOND and NTH Agregate Function

new_aggregates.sql

CREATE TEMPORARY TABLE object_with_cases
(
  id int,
  case int
);

INSERT INTO object_with_cases
  (id, case)
VALUES
  (3, 1)
  (1, 2)
  (2, 5)
  (1, 6)
  (2, 4)
  (3, 3)
  (1, 4)
;

SELECT
    id
  , FIRST(case)  AS FST
  , SECOND(case) AS SND
  , NTH(3, case) AS TRD
FROM object_with_cases
GROUP BY id
ORDER BY case
;

-- OUTPUT

-- | id | FST | SND |  TRD |
-- |  1 |   2 |   4 |    6 | 
-- |  2 |   4 |   5 | NULL |
-- |  3 |   1 |   3 | NULL |