Help Center/ GaussDB/ Developer Guide(Centralized_2.x)/ SQL Reference/ Full Text Search/ Dictionaries/ Synonym Dictionary
Updated on 2023-10-23 GMT+08:00
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Synonym Dictionary

A Synonym dictionary is used to define, identify, and convert synonyms of a token. Phrases are not supported. Synonyms of phrases can be defined in a Thesaurus dictionary. For details, see Thesaurus Dictionary.

Examples

  • A Synonym dictionary can be used to overcome linguistic problems. For example, to prevent an English stemmer dictionary from reducing the word 'Paris' to 'pari', define a Paris paris line in the Synonym dictionary and put it before the english_stem dictionary. 
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    openGauss=# SELECT * FROM ts_debug('english', 'Paris');
   alias   |   description   | token |  dictionaries  |  dictionary  | lexemes 
-----------+-----------------+-------+----------------+--------------+---------
 asciiword | Word, all ASCII | Paris | {english_stem} | english_stem | {pari}
(1 row)

openGauss=# CREATE TEXT SEARCH DICTIONARY my_synonym (
    TEMPLATE = synonym,
    SYNONYMS = my_synonyms,
    FILEPATH = 'file:///home/dicts/' 
);

openGauss=# ALTER TEXT SEARCH CONFIGURATION english
    ALTER MAPPING FOR asciiword
    WITH my_synonym, english_stem;

openGauss=# SELECT * FROM ts_debug('english', 'Paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
(1 row)

openGauss=# SELECT * FROM ts_debug('english', 'paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
(1 row)

openGauss=# ALTER TEXT SEARCH DICTIONARY my_synonym ( CASESENSITIVE=true);

openGauss=# SELECT * FROM ts_debug('english', 'Paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
(1 row)

openGauss=# SELECT * FROM ts_debug('english', 'paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {pari}
(1 row)

    The full name of the Synonym dictionary file is my_synonyms.syn, and the dictionary is stored in the /home/dicts/ directory of the current database primary node. For details about the syntax and parameters for creating an Ispell dictionary, see ALTER TEXT SEARCH DICTIONARY.

  • An asterisk (*) can be placed at the end of a synonym in the configuration file. This indicates that the synonym is a prefix. The asterisk is ignored when the entry is used in to_tsvector(), but when it is used in to_tsquery(), the result will be a query item with the prefix match marker (see Manipulating Queries).

    Assume that the content in the dictionary file synonym_sample.syn is as follows:

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    postgres        pgsql
postgresql      pgsql 
postgre pgsql 
gogle   googl 
indices index*

    Create and use a dictionary.

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    openGauss=# CREATE TEXT SEARCH DICTIONARY syn (
    TEMPLATE = synonym,
    SYNONYMS = synonym_sample
);

openGauss=# SELECT ts_lexize('syn','indices');
 ts_lexize 
-----------
 {index}
(1 row)

openGauss=# CREATE TEXT SEARCH CONFIGURATION tst (copy=simple);

openGauss=# ALTER TEXT SEARCH CONFIGURATION tst ALTER MAPPING FOR asciiword WITH syn;

openGauss=# SELECT to_tsvector('tst','indices');
 to_tsvector 
-------------
 'index':1
(1 row)

openGauss=# SELECT to_tsquery('tst','indices');
 to_tsquery 
------------
 'index':*
(1 row)

openGauss=# SELECT 'indexes are very useful'::tsvector;
            tsvector             
---------------------------------
 'are' 'indexes' 'useful' 'very'
(1 row)

openGauss=# SELECT 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
 ?column? 
----------
 t
(1 row)
Parent topic: Dictionaries