• Data Warehouse Service

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  6. Searching a Table

Searching a Table

It is possible to do a full text search without an index.

  • A simple query to print each row that contains the word america in its body column is as follows:
    DROP SCHEMA IF EXISTS tsearch CASCADE;
    
    CREATE SCHEMA tsearch;
    
    CREATE TABLE tsearch.pgweb(id int, body text, title text, last_mod_date date);
    
    INSERT INTO tsearch.pgweb VALUES(1, 'China, officially the People''s Republic of China (PRC), located in Asia, is the world''s most populous state.', 'China', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(2, 'America is a rock band, formed in England in 1970 by multi-instrumentalists Dewey Bunnell, Dan Peek, and Gerry Beckley.', 'America', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(3, 'England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west.', 'England', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(4, 'Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands.', 'Australia', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(5, 'Russia, also officially known as the Russian Federation, is a sovereign state in northern Eurasia.', 'Russia', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(6, 'Japan is an island country in East Asia.', 'Japan', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(7, 'Germany, officially the Federal Republic of Germany, is a sovereign state and federal parliamentary republic in central-western Europe.', 'Germany', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(8, 'France, is a sovereign state comprising territory in western Europe and several overseas regions and territories.', 'France', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(9, 'Italy officially the Italian Republic, is a unitary parliamentary republic in Europe.', 'Italy', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(10, 'India, officially the Republic of India, is a country in South Asia.', 'India', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(11, 'Brazil, officially the Federative Republic of Brazil, is the largest country in both South America and Latin America.', 'Brazil', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(12, 'Canada is a country in the northern half of North America.', 'Canada', '2010-1-1');
    
    INSERT INTO tsearch.pgweb VALUES(13, 'Mexico, officially the United Mexican States, is a federal republic in the southern part of North America.', 'Mexico', '2010-1-1');
    
    SELECT id, body, title FROM tsearch.pgweb WHERE to_tsvector('english', body) @@ to_tsquery('english', 'america');
     id |                                                          body                                                           |  title  
    ----+-------------------------------------------------------------------------------------------------------------------------+---------
      2 | America is a rock band, formed in England in 1970 by multi-instrumentalists Dewey Bunnell, Dan Peek, and Gerry Beckley. | America
     12 | Canada is a country in the northern half of North America.                                                              | Canada
     13 | Mexico, officially the United Mexican States, is a federal republic in the southern part of North America.              | Mexico
     11 | Brazil, officially the Federative Republic of Brazil, is the largest country in both South America and Latin America.   | Brazil
    (4 rows)

    This will also find related words, such as America, since all these are reduced to the same normalized lexeme.

    The query above specifies that the english configuration is to be used to parse and normalize the strings. Alternatively we could omit the configuration parameters, and use the configuration set by default_text_search_config.

    SHOW default_text_search_config;
     default_text_search_config 
    ----------------------------
     pg_catalog.english
    (1 row)
    
    SELECT id, body, title FROM tsearch.pgweb WHERE to_tsvector(body) @@ to_tsquery('america');
     id |                                                          body                                                           |  title  
    ----+-------------------------------------------------------------------------------------------------------------------------+---------
     11 | Brazil, officially the Federative Republic of Brazil, is the largest country in both South America and Latin America.   | Brazil
      2 | America is a rock band, formed in England in 1970 by multi-instrumentalists Dewey Bunnell, Dan Peek, and Gerry Beckley. | America
     12 | Canada is a country in the northern half of North America.                                                              | Canada
     13 | Mexico, officially the United Mexican States, is a federal republic in the southern part of North America.              | Mexico
    (4 rows)
  • A more complex example to select the ten most recent documents that contain north and america in the title or body column is as follows:
    SELECT title FROM tsearch.pgweb WHERE to_tsvector(title || ' ' || body) @@ to_tsquery('north & america') ORDER BY last_mod_date DESC LIMIT 10;
     title  
    --------
     Mexico
     Canada
    (2 rows)

    For clarity we omitted the coalesce function calls which would be needed to find rows that contain NULL in one of the two columns.

    The preceding examples show queries without using indexes. Most applications will find this approach too slow. Therefore, practical use of text searching usually requires creating an index, except perhaps for occasional ad-hoc searches.