DECLARE @temp TABLE (
ss1 INT PRIMARY KEY,
ss5 INT
)
INSERT INTO @temp (ss1, ss5)
VALUES
(1, 3456), (2, 3333),
(3, 4666), (4, 6744),
(50, NULL), (51, 4578),
(52, 3333), (53, NULL)
SELECT *
FROM (
SELECT *, cnt = COUNT(*) OVER (PARTITION BY ss5)
FROM @temp
WHERE ss5 IS NOT NULL
) t
WHERE t.cnt > 1
Погуглите оконные функции.