SET enable_seqscan to false;
-- test search for "not equals"
CREATE TABLE test_ne (
   a  TIMESTAMP,
   b  NUMERIC
);
CREATE INDEX test_ne_idx ON test_ne USING gist (a, b);
INSERT INTO test_ne SELECT '2009-01-01', 10.7 FROM generate_series(1,1000);
INSERT INTO test_ne VALUES('2007-02-03', -91.3);
INSERT INTO test_ne VALUES('2011-09-01', 43.7);
INSERT INTO test_ne SELECT '2009-01-01', 10.7 FROM generate_series(1,1000);
SET enable_indexscan to false;
EXPLAIN (COSTS OFF) SELECT * FROM test_ne WHERE a <> '2009-01-01' AND b <> 10.7;
                                              QUERY PLAN                                              
------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on test_ne
   Recheck Cond: ((a <> 'Thu Jan 01 00:00:00 2009'::timestamp without time zone) AND (b <> 10.7))
   ->  Bitmap Index Scan on test_ne_idx
         Index Cond: ((a <> 'Thu Jan 01 00:00:00 2009'::timestamp without time zone) AND (b <> 10.7))
(4 rows)

SELECT * FROM test_ne WHERE a <> '2009-01-01' AND b <> 10.7;
            a             |   b   
--------------------------+-------
 Sat Feb 03 00:00:00 2007 | -91.3
 Thu Sep 01 00:00:00 2011 |  43.7
(2 rows)

RESET enable_indexscan;
-- test search for "not equals" using an exclusion constraint
CREATE TABLE zoo (
   cage   INTEGER,
   animal TEXT,
   EXCLUDE USING gist (cage WITH =, animal WITH <>)
);
INSERT INTO zoo VALUES(123, 'zebra');
INSERT INTO zoo VALUES(123, 'zebra');
INSERT INTO zoo VALUES(123, 'lion');
ERROR:  conflicting key value violates exclusion constraint "zoo_cage_animal_excl"
DETAIL:  Key (cage, animal)=(123, lion) conflicts with existing key (cage, animal)=(123, zebra).
INSERT INTO zoo VALUES(124, 'lion');