<programlisting>

CREATE INDEX pgweb_idx ON pgweb USING gin(to_tsvector('english', body));

</programlisting>

Notice that the 2-argument version of <function>to_tsvector</function> is

used. Only text search functions which specify a configuration name can

be used in expression indexes (<xref linkend="indexes-expressional">).

column current anytime <literal>title</> or <literal>body</> changes.

Keep in mind that, just like with expression indexes, it is important to

specify the configuration name when creating text search data types

inside triggers so the column's contents are not affected by changes to

inside triggers so the column's contents are not affected by changes to

<varname>default_text_search_config</>.

</para>

</programlisting>

</para>

<para>

<para>

In the example above we see that the resulting <type>tsvector</type> does not

contain the words <literal>a</literal>, <literal>on</literal>, or

<literal>it</literal>, the word <literal>rats</literal> became

<literal>rat</literal>, and the punctuation sign <literal>-</literal> was

ignored.

</para>

ignored.

</para>

<para>

The <function>to_tsvector</function> function internally calls a parser

<programlisting>

SELECT * FROM ts_debug('english','a fat cat sat on a mat - it ate a fat rats');

Alias | Description | Token | Dictionaries | Lexized token

Alias | Description | Token | Dictionaries | Lexized token

-------+---------------+-------+--------------+----------------

lword | Latin word | a | {english} | english: {}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | fat | {english} | english: {fat}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | cat | {english} | english: {cat}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | sat | {english} | english: {sat}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | on | {english} | english: {}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | a | {english} | english: {}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | mat | {english} | english: {mat}

blank | Space symbols | | |

blank | Space symbols | - | |

blank | Space symbols | | |

blank | Space symbols | - | |

lword | Latin word | it | {english} | english: {}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | ate | {english} | english: {ate}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | a | {english} | english: {}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | fat | {english} | english: {fat}

blank | Space symbols | | |

blank | Space symbols | | |

lword | Latin word | rats | {english} | english: {rat}

(24 rows)

</programlisting>

<programlisting>

{D-weight, C-weight, B-weight, A-weight}

</programlisting>

If no weights are provided,

then these defaults are used:

a b &lt;b&gt;c&lt;/b&gt;

SELECT ts_headline('a b c', 'c'::tsquery, 'StartSel=&lt;,StopSel=&gt;');

ts_headline

ts_headline

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

a b &lt;c&gt;

</programlisting>

</para>

<para>

Some examples of normalization:

Some examples of normalization:

<itemizedlist spacing="compact" mark="bullet">

Linguistic - ispell dictionaries try to reduce input words to a

normalized form; stemmer dictionaries remove word endings

</para>

</listitem>

</listitem>

<listitem>

<para>

Identical <acronym>URL</acronym> locations are identified and canonicalized:

<sect2 id="textsearch-stopwords">

<title>Stop Words</title>

<para>

Stop words are words which are very common, appear in almost

every document, and have no discrimination value. Therefore, they can be ignored

<programlisting>

SELECT * FROM ts_debug('english','Paris');

Alias | Description | Token | Dictionaries | Lexized token

Alias | Description | Token | Dictionaries | Lexized token

-------+-------------+-------+----------------+----------------------

lword | Latin word | Paris | {english_stem} | english_stem: {pari}

(1 row)

ALTER MAPPING FOR lword WITH synonym, english_stem;

SELECT * FROM ts_debug('english','Paris');

Alias | Description | Token | Dictionaries | Lexized token

Alias | Description | Token | Dictionaries | Lexized token

-------+-------------+-------+------------------------+------------------

lword | Latin word | Paris | {synonym,english_stem} | synonym: {paris}

(1 row)

<secondary>GiST</secondary>

</indexterm>

<!--

<indexterm zone="textsearch-indexes">

<primary>GiST</primary>

<secondary>text search</secondary>

</indexterm>

-->

<term>

<synopsis>

CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable> USING gist(<replaceable>column</replaceable>);

<secondary>GIN</secondary>

</indexterm>

<!--

<indexterm zone="textsearch-indexes">

<primary>GIN</primary>

<secondary>text search</secondary>

</indexterm>

<term>

<synopsis>

CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable> USING gin(<replaceable>column</replaceable>);

List of fulltext configurations

Schema | Name | Description

----------+----------------------------

fulltext | fulltext_cfg |

fulltext | fulltext_cfg |

public | fulltext_cfg |

</programlisting>

</para>

PG_FREE_IF_COPY(in, 0);

pcfg=cfg;

while (pcfg-&gt;key)

while (pcfg-&gt;key)

{

if (strcasecmp("MAXLEN", pcfg-&gt;key) == 0)

d-&gt;maxlen=atoi(pcfg-&gt;value);

else if ( strcasecmp("REJECTLONG", pcfg-&gt;key) == 0)

else if ( strcasecmp("REJECTLONG", pcfg-&gt;key) == 0)

{

if ( strcasecmp("true", pcfg-&gt;value) == 0 )

d-&gt;rejectlong=true;

if (PG_GETARG_INT32(2) &gt; d-&gt;maxlen)

{

if (d-&gt;rejectlong)

if (d-&gt;rejectlong)

{ /* stop, return void array */

pfree(txt);

res[0].lexeme = NULL;

/* blank type */

type = 12;

/* go to the next non-white-space character */

while ((pst-&gt;buffer)[pst-&gt;pos] == ' ' &amp;&amp;

while ((pst-&gt;buffer)[pst-&gt;pos] == ' ' &amp;&amp;

pst-&gt;pos &lt; pst-&gt;len)

(pst-&gt;pos)++;

} else {

/* word type */

type = 3;

/* go to the next white-space character */

while ((pst-&gt;buffer)[pst-&gt;pos] != ' ' &amp;&amp;

while ((pst-&gt;buffer)[pst-&gt;pos] != ' ' &amp;&amp;

pst-&gt;pos &lt; pst-&gt;len)

(pst-&gt;pos)++;

}