set enable_seqscan=off;
CREATE TABLE test_oid (
	i oid
);
INSERT INTO test_oid VALUES (0),(1),(2),(3),(4),(5);
CREATE INDEX idx_oid ON test_oid USING gin (i);
SELECT * FROM test_oid WHERE i<3::oid ORDER BY i;
 i 
---
 0
 1
 2
(3 rows)

SELECT * FROM test_oid WHERE i<=3::oid ORDER BY i;
 i 
---
 0
 1
 2
 3
(4 rows)

SELECT * FROM test_oid WHERE i=3::oid ORDER BY i;
 i 
---
 3
(1 row)

SELECT * FROM test_oid WHERE i>=3::oid ORDER BY i;
 i 
---
 3
 4
 5
(3 rows)

SELECT * FROM test_oid WHERE i>3::oid ORDER BY i;
 i 
---
 4
 5
(2 rows)

