An unaccent dictionary accepts the following options:

The rules file has the following format:

A more complete example, which is directly useful for most European languages, can be found in unaccent.rules, which is installed in $SHAREDIR/tsearch_data/ when the unaccent 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).

Installing the unaccent extension creates a text search template unaccent and a dictionary unaccent based on it. The unaccent dictionary has the default parameter setting RULES='unaccent', which makes it immediately usable with the standard unaccent.rules file. If you wish, you can alter the parameter, for example

mydb=# ALTER TEXT SEARCH DICTIONARY unaccent (RULES='my_rules');

or create new dictionaries based on the template.

To test the dictionary, you can try:

mydb=# select ts_lexize('unaccent','Hôtel');
 ts_lexize
-----------
 {Hotel}
(1 row)

Here is an example showing how to insert the unaccent dictionary into a text search configuration:

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)

The unaccent() function removes accents (diacritic signs) from a given string. Basically, it's a wrapper around unaccent-type dictionaries, but it can be used outside normal text search contexts.

unaccent([dictionary regdictionary, ] string text) returns text

If the dictionary argument is omitted, the text search dictionary named unaccent and appearing in the same schema as the unaccent() function itself is used.

For example:

SELECT unaccent('unaccent', 'Hôtel');
SELECT unaccent('Hôtel');