Oracle从7.3开始支持全文检索，即用户可以使用Oracle服务器的上下文（ConText）选项完 成基于文本的查询。具体可以采用通配符查找、模糊匹配、相关分类、近似查找、条件加权和词意扩充等方法。在Oracle8.0.x中 称为ConText ；在Oracle8i中 称为interMedia Text ； Oracle9i以后称为Oracle Text。下面通过示例了解一下oracle全文检索。
分派用户相应权限
grant connect,resource to scott;
grant ctxapp to scott;
alter user portal default role all;
--对象权限
grant execute on ctx_ddl to scott;
解锁ctxsys用户
alter user ctxsys account unlock identified by ctxsys;
用应用用户登录,设置搜索器类型
SQL> conn scott/tiger;
BEGIN
ctx_ddl.create_preference ('main_lexer','CHINESE_LEXER');
ctx_ddl.create_preference('mywordlist', 'BASIC_WORDLIST');
ctx_ddl.set_attribute('mywordlist','PREFIX_INDEX','TRUE');
ctx_ddl.set_attribute('mywordlist','PREFIX_MIN_LENGTH',1);
ctx_ddl.set_attribute('mywordlist','PREFIX_MAX_LENGTH', 5);
ctx_ddl.set_attribute('mywordlist','SUBSTRING_INDEX', 'YES');
END;
/
这里说一下词法分析器(lexer) ，词法分析器有三种：
1）basic_lexer: 针对英语。它能根据空格和标点来 将英语单词从句子中分离，还能自动将一些出现频率过高已经失去检索意义的单词作为‘垃圾’处理，如if , is 等，具有较高的处理效率。但只认空格和标点，而汉语的一句话中通常不会有空格，会把整句话作为一个组,事实上失去检索能力。
2）chinese_vgram_lexer: 专门的汉语分析器，支持所有汉字 字符集（ZHS16CGB231280 ZHS16GBK ZHT32EUC ZHT16BIG5 ZHT32TRIS ZHT16MSWIN950 ZHT16HKSCS UTF8 ）。但分词方法太简单，每个组合都作为一个词，既占用空间又效率不高。
3）chinese_lexer: 这是一个新的汉语分析器，只支持utf8字符集。chinese_lexer的最大改进就是能认识大部分常用汉语词汇，因此能更有效率地分析句子。
创建示例数据
create table docs( id number, name varchar2(200), address varchar2(2000) );
insert into docs values(1,'John Smith','Room 403,No.37,ShiFan Residential Quarter,BaoShan District');
insert into docs values(2,'Noah Abelard','Room 201,No.34,Lane 125,XiKang Road(South),HongKou District');
insert into docs values(3,'Michael Cole','Room 42， Zhongzhou Road，Nanyang City， Henan Prov. ');
insert into docs values(4,'Thomas Matthew','Hongyuan Hotel, Jingzhou city, Hubei Prov. ');
insert into docs values(5,'Joseph','Special Steel Corp，No.272， Bayi Road，Nanyang City， Henan Prov. ');
insert into docs values(6,'Lauren','Room 702, 7th Building, Hengda Garden, East District, Zhongshan ');
insert into docs values(7,'Kevin Victoria','Room 601, No.34 Long Chang Li, Xiamen, Fujian ');
insert into docs values(8,'Michael','Cheng Nuo Ban, Gong Jiao Zong Gong Si, Xiamen, Fujian ');
insert into docs values(9,'Timothy Katherine','NO. 204,Entrance A, Building NO. 1, The 2nd Dormitory of the NO. 4 State-owned Textile Factory, 53 Kaiping Road, Qingdao, Shandong');
insert into docs values(10,'Zhou Wangcai','Room 601, No.34 Long Chang Li,Xiamen, Fujian, China 361012');
insert into docs values(11,'Sebastian Jared','Cheng Nuo Ban, Gong Jiao Zong Gong SiXiamen, Fujian, China 361004');
insert into docs values(12,'Jenna','NO. 204, A, Building NO. 1,The 2nd Dormitory of the NO. 4 State-owned Textile Factory,53 Kaiping Road, Qingdao,Shandong, China 266042 ');
insert into docs values(13,'Catherine','Room403,No.37,SiFanResidentialQuarter,BaoShanDistrict');
insert into docs values(14,'Sebastian Cole','1 Team CaiQi ChuanXiBei Mining Area JiangYou City SiChuan Province China');
insert into docs values(15,'Timothy Jared ','Room 201,No.34,Lane 125,XiKang Road(South),HongKou District');
insert into docs values(16,'张三','中国北京朝阳区北小营亚运花园1号楼8B');
insert into docs values(17,'李四','上海世纪大道1500号9楼');
insert into docs values(18,'王五','四川成都经济技术开发区世纪大道515号');
/
对文本列建立文档CONTEXT索引，并且指定搜索器/过滤器/单词列表/
CREATE INDEX idx_docs_address ON docs(address)
indextype is ctxsys.context parameters
('DATASTORE CTXSYS.DIRECT_DATASTORE FILTER CTXSYS.INSO_FILTER LEXER main_lexer WORDLIST mywordlist');