WITH cte AS
(
SELECT id, wbuser_id, amount
FROM
(
VALUES
(1,1,1.0),
(2,1,5.0),
(3,1,5.0),
(4,1,4.0),
(5,1,4.0),
(6,2,4.0),
(7,2,3.0)
) t (id, wbuser_id, amount)
)
SELECT MIN(
cte.id) id, cte.wbuser_id, cte.amount
FROM cte
LEFT JOIN cte cte2
ON cte2.amount > cte.amount
AND cte2.wbuser_id = cte.wbuser_id
WHERE
cte2.id IS NULL
GROUP by cte.wbuser_id, cte.amount
ORDER BY MIN(
cte.id)