本章节主要介绍如何使用文本搜索运算符搜索数据库表。

• 一个简单查询：将body字段中包含science的每一行打印出来。

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  DROP SCHEMA IF EXISTS tsearch CASCADE; CREATE SCHEMA tsearch; CREATE TABLE tsearch.pgweb(id int, body text, title text, last_mod_date date); INSERT INTO tsearch.pgweb VALUES(1, 'Philology is the study of words, especially the history and development of the words in a particular language or group of languages.', 'Philology', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(2, 'Mathematics is the science that deals with the logic of shape, quantity and arrangement.', 'Mathematics', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(3, 'Computer science is the study of processes that interact with data and that can be represented as data in the form of programs.', 'Computer science', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(4, 'Chemistry is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions.', 'Chemistry', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(5, 'Geography is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets.', 'Geography', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(6, 'History is a subject studied in schools, colleges, and universities that deals with events that have happened in the past.', 'History', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(7, 'Medical science is the science of dealing with the maintenance of health and the prevention and treatment of disease.', 'Medical science', '2010-1-1'); INSERT INTO tsearch.pgweb VALUES(8, 'Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.', 'Physics', '2010-1-1'); SELECT id, body, title FROM tsearch.pgweb WHERE to_tsvector('english', body) @@ to_tsquery('english', 'science'); id | body | title ----+-------------------------------------------------------------------------------------------------------------------------+--------- 2 | Mathematics is the science that deals with the logic of shape, quantity and arrangement. | Mathematics 3 | Computer science is the study of processes that interact with data and that can be represented as data in the form of programs. | Computer science 5 | Geography is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. | Geography 7 | Medical science is the science of dealing with the maintenance of health and the prevention and treatment of disease. | Medical science (4 rows)

  像science这样的相关词都会被找到，因为这些词都被处理成了相同标准的词条。

  上面的查询指定english配置来解析和规范化字符串。也可以省略此配置，通过default_text_search_config进行配置设置：

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  SHOW default_text_search_config; default_text_search_config ---------------------------- pg_catalog.english (1 row) SELECT id, body, title FROM tsearch.pgweb WHERE to_tsvector(body) @@ to_tsquery('science'); id | body | title ----+-------------------------------------------------------------------------------------------------------------------------+--------- 2 | Mathematics is the science that deals with the logic of shape, quantity and arrangement. | Mathematics 3 | Computer science is the study of processes that interact with data and that can be represented as data in the form of programs. | Computer science 5 | Geography is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. | Geography 7 | Medical science is the science of dealing with the maintenance of health and the prevention and treatment of disease. | Medical science (4 rows)

• 一个复杂查询：检索出在title或者body字段中包含treatment和science的最近10篇文档：

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  SELECT title FROM tsearch.pgweb WHERE to_tsvector(title || ' ' || body) @@ to_tsquery('treatment & science') ORDER BY last_mod_date DESC LIMIT 10; title -------- Medical science (1 rows)

  为了清晰，举例中没有调用coalesce函数在两个字段中查找包含NULL的行。

  以上例子均在没有索引的情况下进行查询。对于大多数应用程序来说，这个方法很慢。因此除了偶尔的特定搜索，文本搜索在实际使用中通常需要创建索引。