Работает ли на вашем IBM i следующее "как есть"?
WITH RES (creator, event_id, status, createdTS) AS
(
VALUES
(123, 1, 'New', TIMESTAMP('2019-01-29 17:27:50.899408'))
, (123, 1, 'Live', TIMESTAMP('2019-01-29 17:29:50.899408'))
, (123, 1, 'Closed', TIMESTAMP('2019-01-29 17:45:50.899408'))
, (456, 5, 'New', TIMESTAMP('2019-01-29 17:32:50.899408'))
, (456, 5, 'Live', TIMESTAMP('2019-01-29 17:48:50.899408'))
)
SELECT creator, event_id, status, createdTS
FROM
(
SELECT creator, event_id, status, createdTS
, ROWNUMBER() OVER (PARTITION BY creator ORDER BY createdTS desc) AS rn
FROM RES
) T
WHERE RN=1;
Если нет, то какая у вас версия и модификация IBM i?