CREATE TABLE ids (
  id integer
);
INSERT INTO ids VALUES (2);
INSERT INTO ids VALUES (7);
INSERT INTO ids VALUES (6);
INSERT INTO ids VALUES (4);
INSERT INTO ids VALUES (5);
INSERT INTO ids VALUES (8);
INSERT INTO ids VALUES (1);
INSERT INTO ids VALUES (10);
INSERT INTO ids VALUES (3);
INSERT INTO ids VALUES (9);
CREATE INDEX pgroonga_index ON ids USING pgroonga (id);
SET enable_seqscan = off;
SET enable_indexscan = on;
SET enable_bitmapscan = off;
SELECT id
  FROM ids
 WHERE id IN (6, 1, 7)
 ORDER BY id ASC;
 id 
----
  1
  6
  7
(3 rows)

DROP TABLE ids;