# Synonym词典
Synonym词典用于定义、识别token的同义词并转化，不支持词组（词组形式的同义词可用Thesaurus词典定义，详细请参见[Thesaurus词典](https://support.huaweicloud.com/sqlreference-dws/dws_06_0107.html)）。
#### 示例
- Synonym词典可用于解决语言学相关问题，例如，为避免使单词"Paris"变成"pari"，可在Synonym词典文件中定义一行"Paris paris"，并将该词典放置在预定义的english_stem词典之前。
  ```
  SELECT * FROM ts_debug('english', 'Paris');
     alias   |   description   | token |  dictionaries  |  dictionary  | lexemes 
  -----------+-----------------+-------+----------------+--------------+---------
   asciiword | Word, all ASCII | Paris | {english_stem} | english_stem | {pari}
  (1 row)
  CREATE TEXT SEARCH DICTIONARY my_synonym (
      TEMPLATE = synonym,
      SYNONYMS = my_synonyms,
      FILEPATH =   'obs://bucket01/obs.example.com accesskey=xxxxx secretkey=xxxxx region=cn-north-1'
  );
  ALTER TEXT SEARCH CONFIGURATION english
      ALTER MAPPING FOR asciiword
      WITH my_synonym, english_stem;
  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)
  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)
  ALTER TEXT SEARCH DICTIONARY my_synonym ( CASESENSITIVE=true);
  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)
  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)
  ```
  其中，同义词词典文件全名为my_synonyms.syn，所在目录为 'obs://bucket01/obs.example.com accesskey=xxxxx secretkey=xxxxx region=*cn-north-1* '。关于创建词典的语法和更多参数，请参见[CREATE TEXT SEARCH DICTIONARY](https://support.huaweicloud.com/sqlreference-dws/dws_06_0183.html)。
  
- 星号（\*）可用于词典文件中的同义词结尾，表示该同义词是一个前缀。在to_tsvector()中该星号将被忽略，但在to_tsquery()中会匹配该前缀并对应输出结果（参照[处理查询](https://support.huaweicloud.com/sqlreference-dws/dws_06_0098.html)一节）。
  假设词典文件synonym_sample.syn内容如下：
  ```
  postgres        pgsql
  postgresql      pgsql 
  postgre pgsql 
  gogle   googl 
  indices index*
  ```
  创建并使用词典：
  ```
  CREATE TEXT SEARCH DICTIONARY syn (
      TEMPLATE = synonym,
      SYNONYMS = synonym_sample
  );
  SELECT ts_lexize('syn','indices');
   ts_lexize 
  -----------
   {index}
  (1 row)
  CREATE TEXT SEARCH CONFIGURATION tst (copy=simple);
  ALTER TEXT SEARCH CONFIGURATION tst ALTER MAPPING FOR asciiword WITH syn;
  SELECT to_tsvector('tst','indices');
   to_tsvector 
  -------------
   'index':1
  (1 row)
  SELECT to_tsquery('tst','indices');
   to_tsquery 
  ------------
   'index':*
  (1 row)
  SELECT 'indexes are very useful'::tsvector;
              tsvector             
  ---------------------------------
   'are' 'indexes' 'useful' 'very'
  (1 row)
  SELECT 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
   ?column? 
  ----------
   t
  (1 row)
  ```