SQL Server 2017

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CREATE TABLE maintab
(
  c1 INTEGER,
  c2 INTEGER,
  c3 INTEGER
);

INSERT INTO maintab VALUES(2,  5,  3);
INSERT INTO maintab VALUES(1,  2,  8);
INSERT INTO maintab VALUES(1,  2,  NULL);
INSERT INTO maintab VALUES(1,  4,  7);
INSERT INTO maintab VALUES(2,  4,  8);
INSERT INTO maintab VALUES(1,  3,  NULL);
INSERT INTO maintab VALUES(2,  5,  NULL);
INSERT INTO maintab VALUES(5,  1,  3);
INSERT INTO maintab VALUES(1,  5,  1);
9 rows affected

SELECT * FROM maintab mtx
EXCEPT
SELECT mt1.c1, mt1.c2, mt2.c3
FROM maintab mt1
JOIN maintab mt2
ON mt1.c1 = mt2.c1 AND mt1.c2 = mt2.c2
AND mt1.c3 IS NULL
ORDER BY c1, c2, c3


c1
c2
c3


1
4
7

1
5
1

2
4
8

5
1
3


SELECT c1, c2, c3 
FROM maintab mt
WHERE c3 IS NOT NULL
EXCEPT
SELECT c1, c2, c3 FROM maintab mt
WHERE c1 = 1 AND c2 = 2 AND c3 = 8
ORDER BY c1, c2, c3;


c1
c2
c3


1
4
7

1
5
1

2
4
8

2
5
3

5
1
3