151 lines
3.6 KiB
Plaintext
151 lines
3.6 KiB
Plaintext
<sect1 id="unaccent">
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<title>unaccent</title>
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<indexterm zone="unaccent">
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<primary>unaccent</primary>
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</indexterm>
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<para>
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<filename>unaccent</> removes accents (diacritic signs) from a lexeme.
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It's a filtering dictionary, that means its output is
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always passed to the next dictionary (if any), contrary to the standard
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behavior. Currently, it supports most important accents from european
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languages.
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</para>
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<para>
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Limitation: Current implementation of <filename>unaccent</>
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dictionary cannot be used as a normalizing dictionary for
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<filename>thesaurus</filename> dictionary.
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</para>
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<sect2>
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<title>Configuration</title>
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<para>
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A <literal>unaccent</> dictionary accepts the following options:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<literal>RULES</> is the base name of the file containing the list of
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translation rules. This file must be stored in
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<filename>$SHAREDIR/tsearch_data/</> (where <literal>$SHAREDIR</> means
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the <productname>PostgreSQL</> installation's shared-data directory).
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Its name must end in <literal>.rules</> (which is not to be included in
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the <literal>RULES</> parameter).
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</para>
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</listitem>
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</itemizedlist>
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<para>
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The rules file has the following format:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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Each line represents pair: character_with_accent character_without_accent
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<programlisting>
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À A
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Á A
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 A
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à A
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Ä A
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Å A
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Æ A
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</programlisting>
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</para>
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</listitem>
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</itemizedlist>
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<para>
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Look at <filename>unaccent.rules</>, which is installed in
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<filename>$SHAREDIR/tsearch_data/</>, for an example.
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</para>
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</sect2>
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<sect2>
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<title>Usage</title>
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<para>
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Running the installation script creates a text search template
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<literal>unaccent</> and a dictionary <literal>unaccent</>
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based on it, with default parameters. You can alter the
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parameters, for example
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<programlisting>
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=# ALTER TEXT SEARCH DICTIONARY unaccent (RULES='my_rules');
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</programlisting>
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or create new dictionaries based on the template.
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</para>
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<para>
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To test the dictionary, you can try
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<programlisting>
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=# select ts_lexize('unaccent','Hôtel');
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ts_lexize
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-----------
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{Hotel}
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(1 row)
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</programlisting>
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</para>
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<para>
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Filtering dictionary are useful for correct work of
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<function>ts_headline</function> function.
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<programlisting>
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=# CREATE TEXT SEARCH CONFIGURATION fr ( COPY = french );
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=# ALTER TEXT SEARCH CONFIGURATION fr
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ALTER MAPPING FOR hword, hword_part, word
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WITH unaccent, french_stem;
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=# select to_tsvector('fr','Hôtels de la Mer');
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to_tsvector
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-------------------
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'hotel':1 'mer':4
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(1 row)
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=# select to_tsvector('fr','Hôtel de la Mer') @@ to_tsquery('fr','Hotels');
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?column?
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----------
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t
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(1 row)
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=# select ts_headline('fr','Hôtel de la Mer',to_tsquery('fr','Hotels'));
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ts_headline
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------------------------
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<b>Hôtel</b>de la Mer
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(1 row)
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</programlisting>
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</para>
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</sect2>
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<sect2>
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<title>Function</title>
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<para>
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<function>unaccent</> function removes accents (diacritic signs) from
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argument string. Basically, it's a wrapper around
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<filename>unaccent</> dictionary.
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</para>
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<indexterm>
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<primary>unaccent</primary>
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</indexterm>
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<synopsis>
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unaccent(<optional><replaceable class="PARAMETER">dictionary</replaceable>,
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</optional> <replaceable class="PARAMETER">string</replaceable>)
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returns <type>text</type>
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</synopsis>
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<para>
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<programlisting>
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SELECT unaccent('unaccent','Hôtel');
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SELECT unaccent('Hôtel');
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</programlisting>
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</para>
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</sect2>
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</sect1>
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