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Allow empty replacement strings in contrib/unaccent.

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This is useful in languages where diacritic signs are represented as
separate characters; it's also one step towards letting unaccent be used
for arbitrary substring substitutions.

In passing, improve the user documentation for unaccent, which was sadly
vague about some important details.

Mohammad Alhashash, reviewed by Abhijit Menon-Sen
This commit is contained in:
Tom Lane
2014-06-30 20:51:26 -04:00
parent 55863274d9
commit 97c40ce614
2 changed files with 54 additions and 11 deletions
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36
doc/src/sgml/unaccent.sgml
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@ -45,9 +45,9 @@
<itemizedlist>
<listitem>
<para>
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,
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,
<programlisting>
&Agrave; A
&Aacute; A
@ -57,6 +57,27 @@
&Aring; A
&AElig; A
</programlisting>
The two characters must be separated by whitespace, and any leading or
trailing whitespace on a line is ignored.
</para>
</listitem>
<listitem>
<para>
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.
</para>
</listitem>
<listitem>
<para>
As with other <productname>PostgreSQL</> 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.
</para>
</listitem>
</itemizedlist>
@ -132,8 +153,8 @@ mydb=# select ts_headline('fr','H&ocirc;tel de la Mer',to_tsquery('fr','Hotels')
<para>
The <function>unaccent()</> function removes accents (diacritic signs) from
a given string. Basically, it's a wrapper around the
<filename>unaccent</> dictionary, but it can be used outside normal
a given string. Basically, it's a wrapper around
<filename>unaccent</>-type dictionaries, but it can be used outside normal
text search contexts.
</para>
@ -145,6 +166,11 @@ mydb=# select ts_headline('fr','H&ocirc;tel de la Mer',to_tsquery('fr','Hotels')
unaccent(<optional><replaceable class="PARAMETER">dictionary</replaceable>, </optional> <replaceable class="PARAMETER">string</replaceable>) returns <type>text</type>
</synopsis>
<para>
If the <replaceable class="PARAMETER">dictionary</replaceable> argument is
omitted, <literal>unaccent</> is assumed.
</para>
<para>
For example:
<programlisting>