<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.208 2007/08/29 20:37:14 momjian Exp $ -->

<row>

<entry><type>tsquery</type></entry>

<entry></entry>

<entry>full text search query</entry>

</row>

<row>

<entry><type>tsvector</type></entry>

<entry></entry>

<entry>full text search document</entry>

</row>

<sect1 id="datatype-textsearch">

<title>Full Text Search</title>

<variablelist>

<indexterm zone="datatype-textsearch">

<primary>tsvector</primary>

</indexterm>

<varlistentry>

<term><firstterm>tsvector</firstterm></term>

<listitem>

<para>

<type>tsvector</type> is a data type that represents a document and is

optimized for full text searching. In the simplest case,

<type>tsvector</type> is a sorted list of lexemes, so even without indexes

full text searches perform better than standard <literal>~</literal> and

<literal>LIKE</literal> operations:

<programlisting>

SELECT 'a fat cat sat on a mat and ate a fat rat'::tsvector;

tsvector

----------------------------------------------------

'a' 'on' 'and' 'ate' 'cat' 'fat' 'mat' 'rat' 'sat'

</programlisting>

Notice, that <literal>space</literal> is also a lexeme:

<programlisting>

SELECT 'space '' '' is a lexeme'::tsvector;

tsvector

----------------------------------

'a' 'is' ' ' 'space' 'lexeme'

</programlisting>

Each lexeme, optionally, can have positional information which is used for

<varname>proximity ranking</varname>:

<programlisting>

SELECT 'a:1 fat:2 cat:3 sat:4 on:5 a:6 mat:7 and:8 ate:9 a:10 fat:11 rat:12'::tsvector;

tsvector

-------------------------------------------------------------------------------

'a':1,6,10 'on':5 'and':8 'ate':9 'cat':3 'fat':2,11 'mat':7 'rat':12 'sat':4

</programlisting>

Each lexeme position also can be labeled as <literal>A</literal>,

<literal>B</literal>, <literal>C</literal>, <literal>D</literal>,

where <literal>D</literal> is the default. These labels can be used to group

lexemes into different <emphasis>importance</emphasis> or

<emphasis>rankings</emphasis>, for example to reflect document structure.

Actual values can be assigned at search time and used during the calculation

of the document rank. This is very useful for controlling search results.

</para>

<para>

The concatenation operator, e.g. <literal>tsvector || tsvector</literal>,

can "construct" a document from several parts. The order is important if

<type>tsvector</type> contains positional information. Of course,

it is also possible to build a document using different tables:

<programlisting>

SELECT 'fat:1 cat:2'::tsvector || 'fat:1 rat:2'::tsvector;

?column?

---------------------------

'cat':2 'fat':1,3 'rat':4

SELECT 'fat:1 rat:2'::tsvector || 'fat:1 cat:2'::tsvector;

?column?

---------------------------

'cat':4 'fat':1,3 'rat':2

</programlisting>

</para>

</listitem>

</varlistentry>

<indexterm zone="datatype-textsearch">

<primary>tsquery</primary>

</indexterm>

<varlistentry>

<term><firstterm>tsquery</firstterm></term>

<listitem>

<para>

<type>tsquery</type> is a data type for textual queries which supports

the boolean operators <literal>&amp;</literal> (AND), <literal>|</literal> (OR),

and parentheses. A <type>tsquery</type> consists of lexemes

(optionally labeled by letters) with boolean operators in between:

<programlisting>

SELECT 'fat &amp; cat'::tsquery;

tsquery

---------------

'fat' &amp; 'cat'

SELECT 'fat:ab &amp; cat'::tsquery;

tsquery

------------------

'fat':AB &amp; 'cat'

</programlisting>

Labels can be used to restrict the search region, which allows the

development of different search engines using the same full text index.

</para>

<para>

<type>tsqueries</type> can be concatenated using <literal>&amp;&amp;</literal> (AND)

and <literal>||</literal> (OR) operators:

<programlisting>

SELECT 'a &amp; b'::tsquery &amp;&amp; 'c | d'::tsquery;

?column?

---------------------------

'a' &amp; 'b' &amp; ( 'c' | 'd' )

SELECT 'a &amp; b'::tsquery || 'c|d'::tsquery;

?column?

---------------------------

'a' &amp; 'b' | ( 'c' | 'd' )

</programlisting>

</para>

</listitem>

</varlistentry>

</variablelist>

</sect1>