PostgreSQL 9.1.24 Documentation
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# F.44. unaccent

`unaccent` 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.

The current implementation of `unaccent` cannot be used as a normalizing dictionary for the `thesaurus` dictionary.

## F.44.1. Configuration

An `unaccent` dictionary accepts the following options:

- `RULES` is the base name of the file containing the list of translation rules. This file must be stored in `$SHAREDIR/tsearch_data/` (where `$SHAREDIR` means the PostgreSQL installation's shared-data directory). Its name must end in `.rules` (which is not to be included in the `RULES` parameter).

The rules file has the following format:

- Each line represents a pair, consisting of a character with accent followed by a character without accent. The first is translated into the second. For example,

      À        A
      Á        A
      Â        A
      Ã        A
      Ä        A
      Å        A
      Æ        A

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.

## F.44.2. Usage

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)

## F.44.3. Functions

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

    unaccent([dictionary, ] string) returns text

For example:

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

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