CREATE TABLE memos (
  id integer,
  content text
);

INSERT INTO memos VALUES (1, '');
INSERT INTO memos VALUES (2, 'a');
INSERT INTO memos VALUES (3, 'ab');

CREATE INDEX grnindex ON memos USING pgroonga (content);

SET enable_seqscan = on;
SET enable_indexscan = off;
SET enable_bitmapscan = off;

SELECT id, content
  FROM memos
 WHERE content LIKE '_';

DROP TABLE memos;
