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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.48. unaccent — a text search dictionary which removes diacritics</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="tsm-system-time.html" title="F.47. tsm_system_time — the SYSTEM_TIME sampling method for TABLESAMPLE" /><link rel="next" href="uuid-ossp.html" title="F.49. uuid-ossp — a UUID generator" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.48. unaccent — a text search dictionary which removes diacritics</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="tsm-system-time.html" title="F.47. tsm_system_time — the SYSTEM_TIME sampling method for TABLESAMPLE">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="uuid-ossp.html" title="F.49. uuid-ossp — a UUID generator">Next</a></td></tr></table><hr /></div><div class="sect1" id="UNACCENT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.48. unaccent — a text search dictionary which removes diacritics <a href="#UNACCENT" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="unaccent.html#UNACCENT-CONFIGURATION">F.48.1. Configuration</a></span></dt><dt><span class="sect2"><a href="unaccent.html#UNACCENT-USAGE">F.48.2. Usage</a></span></dt><dt><span class="sect2"><a href="unaccent.html#UNACCENT-FUNCTIONS">F.48.3. Functions</a></span></dt></dl></div><a id="id-1.11.7.58.2" class="indexterm"></a><p>
<code class="filename">unaccent</code> is a text search dictionary that removes accents
(diacritic signs) from lexemes.
It's a filtering dictionary, which means its output is
always passed to the next dictionary (if any), unlike the normal
behavior of dictionaries. This allows accent-insensitive processing
for full text search.
</p><p>
The current implementation of <code class="filename">unaccent</code> cannot be used as a
normalizing dictionary for the <code class="filename">thesaurus</code> dictionary.
</p><p>
This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be
installed by non-superusers who have <code class="literal">CREATE</code> privilege
on the current database.
</p><div class="sect2" id="UNACCENT-CONFIGURATION"><div class="titlepage"><div><div><h3 class="title">F.48.1. Configuration <a href="#UNACCENT-CONFIGURATION" class="id_link">#</a></h3></div></div></div><p>
An <code class="literal">unaccent</code> dictionary accepts the following options:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
<code class="literal">RULES</code> is the base name of the file containing the list of
translation rules. This file must be stored in
<code class="filename">$SHAREDIR/tsearch_data/</code> (where <code class="literal">$SHAREDIR</code> means
the <span class="productname">PostgreSQL</span> installation's shared-data directory).
Its name must end in <code class="literal">.rules</code> (which is not to be included in
the <code class="literal">RULES</code> parameter).
</p></li></ul></div><p>
The rules file has the following format:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
Each line represents one translation rule, consisting of a character with
accent followed by a character without accent. The first is translated
into the second. For example,
</p><pre class="programlisting">
À A
Á A
 A
à A
Ä A
Å A
Æ AE
</pre><p>
The two characters must be separated by whitespace, and any leading or
trailing whitespace on a line is ignored.
</p></li><li class="listitem"><p>
Alternatively, if only one character is given on a line, instances of
that character are deleted; this is useful in languages where accents
are represented by separate characters.
</p></li><li class="listitem"><p>
Actually, each <span class="quote">“<span class="quote">character</span>”</span> can be any string not containing
whitespace, so <code class="filename">unaccent</code> dictionaries could be used for
other sorts of substring substitutions besides diacritic removal.
</p></li><li class="listitem"><p>
As with other <span class="productname">PostgreSQL</span> text search configuration files,
the rules file must be stored in UTF-8 encoding. The data is
automatically translated into the current database's encoding when
loaded. Any lines containing untranslatable characters are silently
ignored, so that rules files can contain rules that are not applicable in
the current encoding.
</p></li></ul></div><p>
A more complete example, which is directly useful for most European
languages, can be found in <code class="filename">unaccent.rules</code>, which is installed
in <code class="filename">$SHAREDIR/tsearch_data/</code> when the <code class="filename">unaccent</code>
module is installed. This rules file translates characters with accents
to the same characters without accents, and it also expands ligatures
into the equivalent series of simple characters (for example, Æ to
AE).
</p></div><div class="sect2" id="UNACCENT-USAGE"><div class="titlepage"><div><div><h3 class="title">F.48.2. Usage <a href="#UNACCENT-USAGE" class="id_link">#</a></h3></div></div></div><p>
Installing the <code class="literal">unaccent</code> extension creates a text
search template <code class="literal">unaccent</code> and a dictionary <code class="literal">unaccent</code>
based on it. The <code class="literal">unaccent</code> dictionary has the default
parameter setting <code class="literal">RULES='unaccent'</code>, which makes it immediately
usable with the standard <code class="filename">unaccent.rules</code> file.
If you wish, you can alter the parameter, for example
</p><pre class="programlisting">
mydb=# ALTER TEXT SEARCH DICTIONARY unaccent (RULES='my_rules');
</pre><p>
or create new dictionaries based on the template.
</p><p>
To test the dictionary, you can try:
</p><pre class="programlisting">
mydb=# select ts_lexize('unaccent','Hôtel');
ts_lexize
-----------
{Hotel}
(1 row)
</pre><p>
</p><p>
Here is an example showing how to insert the
<code class="filename">unaccent</code> dictionary into a text search configuration:
</p><pre class="programlisting">
mydb=# CREATE TEXT SEARCH CONFIGURATION fr ( COPY = french );
mydb=# ALTER TEXT SEARCH CONFIGURATION fr
ALTER MAPPING FOR hword, hword_part, word
WITH unaccent, french_stem;
mydb=# select to_tsvector('fr','Hôtels de la Mer');
to_tsvector
-------------------
'hotel':1 'mer':4
(1 row)
mydb=# select to_tsvector('fr','Hôtel de la Mer') @@ to_tsquery('fr','Hotels');
?column?
----------
t
(1 row)
mydb=# select ts_headline('fr','Hôtel de la Mer',to_tsquery('fr','Hotels'));
ts_headline
------------------------
<b>Hôtel</b> de la Mer
(1 row)
</pre><p>
</p></div><div class="sect2" id="UNACCENT-FUNCTIONS"><div class="titlepage"><div><div><h3 class="title">F.48.3. Functions <a href="#UNACCENT-FUNCTIONS" class="id_link">#</a></h3></div></div></div><p>
The <code class="function">unaccent()</code> function removes accents (diacritic signs) from
a given string. Basically, it's a wrapper around
<code class="filename">unaccent</code>-type dictionaries, but it can be used outside normal
text search contexts.
</p><a id="id-1.11.7.58.8.3" class="indexterm"></a><pre class="synopsis">
unaccent([<span class="optional"><em class="replaceable"><code>dictionary</code></em> <code class="type">regdictionary</code>, </span>] <em class="replaceable"><code>string</code></em> <code class="type">text</code>) returns <code class="type">text</code>
</pre><p>
If the <em class="replaceable"><code>dictionary</code></em> argument is
omitted, the text search dictionary named <code class="literal">unaccent</code> and
appearing in the same schema as the <code class="function">unaccent()</code>
function itself is used.
</p><p>
For example:
</p><pre class="programlisting">
SELECT unaccent('unaccent', 'Hôtel');
SELECT unaccent('Hôtel');
</pre><p>
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