MySQL -- 全文检索(查询扩展检索)

通常用在查询的关键词太短，用户需要隐含知识进行扩展。例如，查单词database时，用户可能还希望不仅仅包含database的文档，可能还指包含mysql、oracle、db2等单词。这时就需要查询扩展。

使用"with query expansion"或"in natural language mode with query expansion"关键语法就可以开启自动相关性反馈。共有两个阶段：
1.根据检索的单词进行全文检索
2.根据第一阶段产生的分词在进行一次全文检索，找出与第一阶段相关性比较高的单词

mysql> SELECT * 
    -> FROM  articles
    -> WHERE
    ->     MATCH (title , body) AGAINST ('database' IN NATURAL LANGUAGE MODE);
+----+-------------------+------------------------------------------+
| id | title             | body                                     |
+----+-------------------+------------------------------------------+
|  5 | MySQL vs. YourSQL | In the following database comparison ... |
|  7 | MySQL Tutorial    | DBMS stands for DataBase ...             |
+----+-------------------+------------------------------------------+
2 rows in set (0.00 sec)

mysql> SELECT  *
    -> FROM  articles
    -> WHERE
    ->     MATCH (title , body) AGAINST ('database' WITH QUERY EXPANSION);
+----+-----------------------+------------------------------------------------------------------+
| id | title                 | body                                                             |
+----+-----------------------+------------------------------------------------------------------+
|  5 | MySQL vs. YourSQL     | In the following database comparison ...                         |
|  7 | MySQL Tutorial        | DBMS stands for DataBase ...                                     |
|  8 | Oracle Tutorial       | DBMS stands for you to test DB ...                               |
|  6 | MySQL Security        | When configured properly, MySQL ...                              |
|  3 | Optimizing MySQL      | In this tutorial we will show ...                                |
|  2 | How To Use MySQL Well | After you went through a ...                                     |
|  4 | 1001 MySQL Tricks     | 1. Never run mysqld as root. 2. ...                              |
| 11 | Python Tutorial       | pthon is ab1 bc2 cd3 de4 ef5 fg6 gh7 hi8 ij9 jk10 kl11 lm12 mn13 |
| 12 | BOOLEN Tutorial       | word1,word2,word3,word4,word5,word6,word7,word8,word9,word10     |
+----+-----------------------+------------------------------------------------------------------+
9 rows in set (0.00 sec)

mysql> 

　　

由于查询扩展可能带来许多非相关性的查询，建议谨慎使用！