This is a document for PGroonga 1.X. See PGroonga 2.x document when you're using recent PGroonga.

LIKE operator

Summary

PGroonga converts column LIKE '%KEYWORD%' condition to column %% 'KEYWORD' internally. %% operator performs full text search with index. It's faster than LIKE operator without index.

column LIKE '%KEYWORD%' with index is slower than column %% 'KEYWORD' with index because column LIKE '%KEYWORD%' with index needs "Recheck". column %% 'KEYWORD' doesn't need "Recheck".

The original LIKE operator searches against text as is. But %% operator performs full text search against normalized text. It means that search result of LIKE operator with index needs "Recheck".

Operator classes

You need to specify one of the following operator classes to use this operator:

Syntax

Here is the syntax of this operator:

column LIKE pattern

column is a column to be searched.

pattern is a search pattern. It's text type.

Usage

Here are sample schema and data for examples:

CREATE TABLE memos (
  id integer,
  content text
);

CREATE INDEX pgroonga_content_index ON memos USING pgroonga (content);

INSERT INTO memos VALUES (1, 'PostgreSQL is a relational database management system.');
INSERT INTO memos VALUES (2, 'Groonga is a fast full text search engine that supports all languages.');
INSERT INTO memos VALUES (3, 'PGroonga is a PostgreSQL extension that uses Groonga as index.');
INSERT INTO memos VALUES (4, 'There is groonga command.');

You can perform LIKE operator with index:

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

SELECT * FROM memos WHERE content LIKE '%groonga%';
--  id |          content          
-- ----+---------------------------
--   4 | There is groonga command.
-- (1 row)

The default operator class of PGroonga index for text type can't find any records with partial alphabet keyword. For example, you can't find record with roonga keyword:

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

SELECT * FROM memos WHERE content LIKE '%roonga%';
--  id | content 
-- ----+---------
-- (0 rows)

But you can find some records with roonga keyword without index:

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

SELECT * FROM memos WHERE content LIKE '%roonga%';
--  id |                                content                                 
-- ----+------------------------------------------------------------------------
--   2 | Groonga is a fast full text search engine that supports all languages.
--   3 | PGroonga is a PostgreSQL extension that uses Groonga as index.
--   4 | There is groonga command.
-- (3 rows)

You can find records by prefix alphabet keyword such as Gro:

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

SELECT * FROM memos WHERE content LIKE '%Gro%';
--  id |                                content                                 
-- ----+------------------------------------------------------------------------
--   2 | Groonga is a fast full text search engine that supports all languages.
--   3 | PGroonga is a PostgreSQL extension that uses Groonga as index.
-- (2 rows)

If you want to search by partial alphabet keyword, there are two approaches.

The first approach is using the TokenBigramSplitSymbolAlphaDigit tokenizer:

DROP INDEX IF EXISTS pgroonga_content_index;

CREATE INDEX pgroonga_content_index
          ON memos
       USING pgroonga (content)
        WITH (tokenizer='TokenBigramSplitSymbolAlphaDigit');

You can find records by roonga:

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

SELECT * FROM memos WHERE content LIKE '%roonga%';
--  id |                                content                                 
-- ----+------------------------------------------------------------------------
--   2 | Groonga is a fast full text search engine that supports all languages.
--   3 | PGroonga is a PostgreSQL extension that uses Groonga as index.
--   4 | There is groonga command.
-- (3 rows)

See Customization in CREATE INDEX USING pgroonga for tokenizer.

The second approach is using pgroonga.text_regexp_ops operator class:

DROP INDEX IF EXISTS pgroonga_content_index;

CREATE INDEX pgroonga_content_index
          ON memos
       USING pgroonga (content pgroonga.text_regexp_ops);

You can find records by rooonga:

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

SELECT * FROM memos WHERE content LIKE '%roonga%';
--  id |                                content                                 
-- ----+------------------------------------------------------------------------
--   2 | Groonga is a fast full text search engine that supports all languages.
--   3 | PGroonga is a PostgreSQL extension that uses Groonga as index.
--   4 | There is groonga command.
-- (3 rows)

See also