sql – tsvector上的“to_tsquery”在使用“简单”和“英文”时

例

> SELECT to_tsvector('mortgag') @@ to_tsquery('simple','mortgage')
?column? 
----------
 f
(1 row)

> SELECT to_tsvector('mortgag') @@ to_tsquery('english','mortgage')
?column? 
----------
 t
(1 row)

我会认为他们都应该返回真的,但显然第一个不是 – 为什么？

解决方法

12.6. Dictionaries

Dictionaries are used to eliminate words that should not be considered in a search (stop words),and to normalize words so that different derived forms of the same word will match. A successfully normalized word is called a lexeme.

因此,字典被用来抛出在搜索(停止单词)中考虑太常见或无意义的东西,并使所有其他内容正常化,例如,即使它们是不同的单词,城市和城市也会匹配.

让我们看一下从ts_debug的一些输出,看看字典发生了什么：

=> select * from ts_debug('english','mortgage');
   alias   |   description   |  token   |  dictionaries  |  dictionary  |  lexemes  
-----------+-----------------+----------+----------------+--------------+-----------
 asciiword | Word,all ASCII | mortgage | {english_stem} | english_stem | {mortgag}

=> select * from ts_debug('simple','mortgage');
   alias   |   description   |  token   | dictionaries | dictionary |  lexemes   
-----------+-----------------+----------+--------------+------------+------------
 asciiword | Word,all ASCII | mortgage | {simple}     | simple     | {mortgage}

请注意,简单使用简单的字典,而英语使用english_stem字典.

simple dictionary：

operates by converting the input token to lower case and checking it against a file of stop words. If it is found in the file then an empty array is returned,causing the token to be discarded. If not,the lower-cased form of the word is returned as the normalized lexeme.

简单的字典只是抛出了停止的单词,下拉菜单,就是这样.我们可以看到自己的简单性：

=> select to_tsquery('simple','Mortgage'),to_tsquery('simple','Mortgages');
 to_tsquery | to_tsquery  
------------+-------------
 'mortgage' | 'mortgages'

简单的字典太简单,甚至不能处理简单的复数.

那么这个english_stem字典是什么？ “茎”后缀是一个放弃：这个字典应用一个词干算法来转换(例如)城市和城市到同一个字.从fine manual：

12.6.6. Snowball Dictionary

The Snowball dictionary template is based on a project by Martin Porter,inventor of the popular Porter’s stemming algorithm for the English language. […] Each algorithm understands how to reduce common variant forms of words to a base,or stem,spelling within its language.

而在下面我们看到english_stem字典：

06002

所以,english_stem字典可以看出,

=> select to_tsquery('english',to_tsquery('english','Mortgages');
 to_tsquery | to_tsquery 
------------+------------
 'mortgag'  | 'mortgag'

执行摘要：“简单”意味着简单的头脑文字匹配,“英语”适用于(希望)产生更好的匹配.结果将抵押贷款转为抵押贷款,并为您提供了匹配.

（编辑：李大同）

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