postgresql/doc/src/sgml/charset.sgml

<!-- $Header: /cvsroot/pgsql/doc/src/sgml/charset.sgml,v 2.36 2003/05/15 15:50:18 petere Exp $ -->

<chapter id="charset">
 <title>Localization</>

 <para>
  This chapter describes the available localization features from the
  point of view of the administrator.
  <productname>PostgreSQL</productname> supports localization with
  three approaches:

   <itemizedlist>
    <listitem>
     <para>
      Using the locale features of the operating system to provide
      locale-specific collation order, number formatting, translated
      messages, and other aspects.
     </para>
    </listitem>

    <listitem>
     <para>
      Providing a number of different character sets defined in the
      <productname>PostgreSQL</productname> server, including
      multiple-byte character sets, to support storing text in all
      kinds of languages, and providing character set recoding between
      client and server.
     </para>
    </listitem>

    <listitem>
     <para>
      Single-byte character recoding provides a more light-weight
      solution for users of multiple, yet single-byte character sets.
     </para>
    </listitem>
   </itemizedlist>
  </para>


 <sect1 id="locale">
  <title>Locale Support</title>
  
  <indexterm zone="locale"><primary>locale</></>

  <para>
   <firstterm>Locale</> support refers to an application respecting
   cultural preferences regarding alphabets, sorting, number
   formatting, etc.  <productname>PostgreSQL</> uses the standard ISO
   C and <acronym>POSIX</acronym> locale facilities provided by the server operating
   system.  For additional information refer to the documentation of your
   system.
  </para>

  <sect2>
   <title>Overview</>

   <para>
    Locale support is automatically initialized when a database
    cluster is created using <command>initdb</command>.
    <command>initdb</command> will initialize the database cluster
    with the locale setting of its execution environment; so if your
    system is already set to use the locale that you want in your
    database cluster then there is nothing else you need to do.  If
    you want to use a different locale (or you are not sure which
    locale your system is set to), you can tell
    <command>initdb</command> exactly which locale you want with the
    option <option>--locale</option>.  For example:
<screen>
initdb --locale=sv_SE
</screen>
   </para>

   <para>
    This example sets the locale to Swedish (<literal>sv</>) as spoken in
    Sweden (<literal>SE</>).  Other possibilities might be
    <literal>en_US</> (U.S. English) and <literal>fr_CA</> (Canada,
    French).  If more than one character set can be useful for a locale
    then the specifications look like this:
    <literal>cs_CZ.ISO8859-2</>. What locales are available under what
    names on your system depends on what was provided by the operating
    system vendor and what was installed.
   </para>

   <para>
    Occasionally it is useful to mix rules from several locales, e.g.,
    use English collation rules but Spanish messages.  To support that, a
    set of locale subcategories exist that control only a certain
    aspect of the localization rules.

    <informaltable>
     <tgroup cols="2">
      <tbody>
       <row>
        <entry><envar>LC_COLLATE</></>
        <entry>String sort order</>
       </row>
       <row>
        <entry><envar>LC_CTYPE</></>
        <entry>Character classification (What is a letter? The upper-case equivalent?)</>
       </row>
       <row>
        <entry><envar>LC_MESSAGES</></>
        <entry>Language of messages</>
       </row>
       <row>
        <entry><envar>LC_MONETARY</></>
        <entry>Formatting of currency amounts</>
       </row>
       <row>
        <entry><envar>LC_NUMERIC</></>
        <entry>Formatting of numbers</>
       </row>
       <row>
        <entry><envar>LC_TIME</></>
        <entry>Formatting of dates and times</>
       </row>
      </tbody>
     </tgroup>
    </informaltable>

    The category names translate into names of
    <command>initdb</command> options to override the locale choice
    for a specific category.  For instance, to set the locale to
    French Canadian, but use U.S. rules for formatting currency, use
    <literal>initdb --locale=fr_CA --lc-monetary=en_US</literal>.
   </para>

   <para>
    If you want the system to behave as if it had no locale support,
    use the special locale <literal>C</> or <literal>POSIX</>.
   </para>

   <para>
    The nature of some locale categories is that their value has to be
    fixed for the lifetime of a database cluster.  That is, once
    <command>initdb</command> has run, you cannot change them anymore.
    <literal>LC_COLLATE</literal> and <literal>LC_CTYPE</literal> are
    those categories.  They affect the sort order of indexes, so they
    must be kept fixed, or indexes on text columns will become corrupt.
    <productname>PostgreSQL</productname> enforces this by recording
    the values of <envar>LC_COLLATE</> and <envar>LC_CTYPE</> that are
    seen by <command>initdb</>.  The server automatically adopts
    those two values when it is started.
   </para>

   <para>
    The other locale categories can be changed as desired whenever the
    server is running by setting the run-time configuration variables
    that have the same name as the locale categories (see <xref
    linkend="runtime-config"> for details).  The defaults that are
    chosen by <command>initdb</command> are actually only written into
    the configuration file <filename>postgresql.conf</filename> to
    serve as defaults when the server is started.  If you delete the
    assignments from <filename>postgresql.conf</filename> then the
    server will inherit the settings from the execution environment.
   </para>

   <para>
    Note that the locale behavior of the server is determined by the
    environment variables seen by the server, not by the environment
    of any client.  Therefore, be careful to configure the correct locale settings
    before starting the server.  A consequence of this is that if
    client and server are set up to different locales, messages may
    appear in different languages depending on where they originated.
   </para>

   <note>
    <para>
     When we speak of inheriting the locale from the execution
     environment, this means the following on most operating systems:
     For a given locale category, say the collation, the following
     environment variables are consulted in this order until one is
     found to be set: <envar>LC_ALL</envar>, <envar>LC_COLLATE</envar>
     (the variable corresponding to the respective category),
     <envar>LANG</envar>.  If none of these environment variables are
     set then the locale defaults to <literal>C</literal>.
    </para>

    <para>
     Some message localization libraries also look at the environment
     variable <envar>LANGUAGE</envar> which overrides all other locale
     settings for the purpose of setting the language of messages.  If
     in doubt, please refer to the documentation of your operating
     system, in particular the documentation about
     <application>gettext</>, for more information.
    </para>
   </note>

   <para>
    To enable messages translated to the user's preferred language,
    <acronym>NLS</acronym> must have been enabled at build time.  This
    choice is independent of the other locale support.
   </para>
  </sect2>

  <sect2>
   <title>Benefits</>

   <para>
    Locale support influences in particular the following features:

    <itemizedlist>
     <listitem>
      <para>
       Sort order in queries using <command>ORDER BY</>
       <indexterm><primary>ORDER BY</></>
      </para>
     </listitem>

     <listitem>
      <para>
       The <function>to_char</> family of functions
      </para>
     </listitem>
    </itemizedlist>
   </para>

   <para>
    The only severe drawback of using the locale support in
    <productname>PostgreSQL</> is its speed.  So use locales only if
    you actually need them.
   </para>
  </sect2>

  <sect2>
   <title>Problems</>

   <para>
    If locale support doesn't work in spite of the explanation above,
    check that the locale support in your operating system is
    correctly configured.  To check what locales are installed on your
    system, you may use the command <literal>locale -a</literal> if
    your operating system provides it.
   </para>

   <para>
    Check that <productname>PostgreSQL</> is actually using the locale
    that you think it is.  <envar>LC_COLLATE</> and <envar>LC_CTYPE</>
    settings are determined at <command>initdb</> time and cannot be
    changed without repeating <command>initdb</>.  Other locale
    settings including <envar>LC_MESSAGES</> and <envar>LC_MONETARY</>
    are initially determined by the environment the server is started
    in.  You can check the <envar>LC_COLLATE</> and <envar>LC_CTYPE</>
    settings of a database with the utility program
    <command>pg_controldata</>.
   </para>

   <para>
    The directory <filename>src/test/locale</> in the source
    distribution contains a test suite for
    <productname>PostgreSQL</>'s locale support.
   </para>

   <para>
    Client applications that handle server-side errors by parsing the
    text of the error message will obviously have problems when the
    server's messages are in a different language.  If you create such
    an application you need to devise a plan to cope with this
    situation.  The embedded SQL interface (<application>ECPG</>) is
    also affected by this problem.  It is currently recommended that
    servers interfacing with <application>ECPG</> applications be
    configured to send messages in English.
   </para>

   <para>
    Maintaining catalogs of message translations requires the on-going
    efforts of many volunteers that want to see
    <productname>PostgreSQL</> speak their preferred language well.
    If messages in your language is currently not available or fully
    translated, your assistance would be appreciated.  If you want to
    help, refer to the <xref linkend="nls"> or write to the developers'
    mailing list.
   </para>
  </sect2>
 </sect1>


 <sect1 id="multibyte">
  <title>Character Set Support</title>

  <indexterm zone="multibyte"><primary>character set</></>

  <para>
   The character set support in <productname>PostgreSQL</productname>
   allows you to store text in a variety of character sets, including
   single-byte character sets such as the ISO 8859 series and
   multiple-byte character sets such as <acronym>EUC</> (Extended Unix
   Code), Unicode, and Mule internal code.  All character sets can be
   used transparently throughout the server.  (If you use extension
   functions from other sources, it depends on whether they wrote
   their code correctly.)  The default character set is selected while
   initializing your <productname>PostgreSQL</productname> database
   cluster using <command>initdb</>.  It can be overridden when you
   create a database using <command>createdb</command> or by using the
   SQL command <command>CREATE DATABASE</>. So you can have multiple
   databases each with a different character set.
  </para>

   <sect2>
    <title>Supported Character Sets</title>

    <para>
     <xref linkend="charset-table"> shows the character sets available
     for use in the server.
    </para>

     <table id="charset-table">
      <title>Server Character Sets</title>
      <tgroup cols="2">
       <thead>
	<row>
	 <entry>Name</entry>
	 <entry>Description</entry>
	</row>
       </thead>
       <tbody>
	<row>
	 <entry><literal>SQL_ASCII</literal></entry>
	 <entry><acronym>ASCII</acronym></entry>
	</row>
	<row>
	 <entry><literal>EUC_JP</literal></entry>
	 <entry>Japanese <acronym>EUC</></entry>
	</row>
	<row>
	 <entry><literal>EUC_CN</literal></entry>
	 <entry>Chinese <acronym>EUC</></entry>
	</row>
	<row>
	 <entry><literal>EUC_KR</literal></entry>
	 <entry>Korean <acronym>EUC</></entry>
	</row>
	<row>
	 <entry><literal>JOHAB</literal></entry>
	 <entry>Korean <acronym>EUC</> (Hangle base)</entry>
	</row>
	<row>
	 <entry><literal>EUC_TW</literal></entry>
	 <entry>Taiwan <acronym>EUC</acronym></entry>
	</row>
	<row>
	 <entry><literal>UNICODE</literal></entry>
	 <entry>Unicode (<acronym>UTF</acronym>-8)</entry>
	</row>
	<row>
	 <entry><literal>MULE_INTERNAL</literal></entry>
	 <entry>Mule internal code</entry>
	</row>
	<row>
	 <entry><literal>LATIN1</literal></entry>
	 <entry>ISO 8859-1/<acronym>ECMA</> 94 (Latin alphabet no.1)</entry>
	</row>
	<row>
	 <entry><literal>LATIN2</literal></entry>
	 <entry>ISO 8859-2/<acronym>ECMA</> 94 (Latin alphabet no.2)</entry>
	</row>
	<row>
	 <entry><literal>LATIN3</literal></entry>
	 <entry>ISO 8859-3/<acronym>ECMA</> 94 (Latin alphabet no.3)</entry>
	</row>
	<row>
	 <entry><literal>LATIN4</literal></entry>
	 <entry>ISO 8859-4/<acronym>ECMA</> 94 (Latin alphabet no.4)</entry>
	</row>
	<row>
	 <entry><literal>LATIN5</literal></entry>
	 <entry>ISO 8859-9/<acronym>ECMA</> 128 (Latin alphabet no.5)</entry>
	</row>
	<row>
	 <entry><literal>LATIN6</literal></entry>
	 <entry>ISO 8859-10/<acronym>ECMA</> 144 (Latin alphabet no.6)</entry>
	</row>
	<row>
	 <entry><literal>LATIN7</literal></entry>
	 <entry>ISO 8859-13 (Latin alphabet no.7)</entry>
	</row>
	<row>
	 <entry><literal>LATIN8</literal></entry>
	 <entry>ISO 8859-14 (Latin alphabet no.8)</entry>
	</row>
	<row>
	 <entry><literal>LATIN9</literal></entry>
	 <entry>ISO 8859-15 (Latin alphabet no.9)</entry>
	</row>
	<row>
	 <entry><literal>LATIN10</literal></entry>
	 <entry>ISO 8859-16/<acronym>ASRO</> SR 14111 (Latin alphabet no.10)</entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_5</literal></entry>
	 <entry>ISO 8859-5/<acronym>ECMA</> 113 (Latin/Cyrillic)</entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_6</literal></entry>
	 <entry>ISO 8859-6/<acronym>ECMA</> 114 (Latin/Arabic)</entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_7</literal></entry>
	 <entry>ISO 8859-7/<acronym>ECMA</> 118 (Latin/Greek)</entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_8</literal></entry>
	 <entry>ISO 8859-8/<acronym>ECMA</> 121 (Latin/Hebrew)</entry>
	</row>
	<row>
	 <entry><literal>KOI8</literal></entry>
	 <entry><acronym>KOI</acronym>8-R(U)</entry>
	</row>
	<row>
	 <entry><literal>WIN</literal></entry>
	 <entry>Windows CP1251</entry>
	</row>
	<row>
	 <entry><literal>ALT</literal></entry>
	 <entry>Windows CP866</entry>
	</row>
	<row>
	 <entry><literal>WIN1256</literal></entry>
	 <entry>Windows CP1256 (Arabic)</entry>
	</row>
	<row>
	 <entry><literal>TCVN</literal></entry>
	 <entry><acronym>TCVN</>-5712/Windows CP1258 (Vietnamese)</entry>
	</row>
	<row>
	 <entry><literal>WIN874</literal></entry>
	 <entry>Windows CP874 (Thai)</entry>
	</row>
       </tbody>
      </tgroup>
     </table>

    <important>
     <para>
      Before <productname>PostgreSQL</> 7.2, <literal>LATIN5</>
      mistakenly meant ISO 8859-5.  From 7.2 on, <literal>LATIN5</>
      means ISO 8859-9. If you have a <literal>LATIN5</> database
      created on 7.1 or earlier and want to migrate to 7.2 or later,
      you should be very careful about this change.
     </para>
    </important>

     <para>
      Not all <acronym>API</>s support all the listed character sets. For example, the
      <productname>PostgreSQL</>
      JDBC driver does not support <literal>MULE_INTERNAL</>, <literal>LATIN6</>,
      <literal>LATIN8</>, and <literal>LATIN10</>.
     </para>
    </sect2>
    
   <sect2>
    <title>Setting the Character Set</title>

    <para>
     <command>initdb</> defines the default character set
     for a <productname>PostgreSQL</productname> cluster. For example,

<screen>
initdb -E EUC_JP
</screen>

     sets the default character set (encoding) to
     <literal>EUC_JP</literal> (Extended Unix Code for Japanese).  You
     can use <option>--encoding</option> instead of
     <option>-E</option> if you prefer to type longer option strings.
     If no <option>-E</> or <option>--encoding</option> option is
     given, <literal>SQL_ASCII</> is used.
    </para>

    <para>
     You can create a database with a different character set:

<screen>
createdb -E EUC_KR korean
</screen>

     This will create a database named <literal>korean</literal> that
     uses the character set <literal>EUC_KR</literal>.  Another way to
     accomplish this is to use this SQL command:

<programlisting>
CREATE DATABASE korean WITH ENCODING 'EUC_KR';
</programlisting>

     The encoding for a database is stored in the system catalog
     <literal>pg_database</literal>.  You can see that by using the
     <option>-l</option> option or the <command>\l</command> command
     of <command>psql</command>.

<screen>
$ <userinput>psql -l</userinput>
            List of databases
   Database    |  Owner  |   Encoding    
---------------+---------+---------------
 euc_cn        | t-ishii | EUC_CN
 euc_jp        | t-ishii | EUC_JP
 euc_kr        | t-ishii | EUC_KR
 euc_tw        | t-ishii | EUC_TW
 mule_internal | t-ishii | MULE_INTERNAL
 regression    | t-ishii | SQL_ASCII
 template1     | t-ishii | EUC_JP
 test          | t-ishii | EUC_JP
 unicode       | t-ishii | UNICODE
(9 rows)
</screen>
    </para>
   </sect2>

   <sect2>
    <title>Automatic Character Set Conversion Between Server and Client</title>

    <para>
     <productname>PostgreSQL</productname> supports automatic
     character set conversion between server and client for certain
     character sets. The conversion information is stored in the
     <literal>pg_conversion</> system catalog. You can create a new
     conversion by using the SQL command <command>CREATE
     CONVERSION</command>. <productname>PostgreSQL</> comes with some
     predefined conversions. They are listed in <xref
     linkend="multibyte-translation-table">.
    </para>

     <table id="multibyte-translation-table">
      <title>Client/Server Character Set Conversions</title>
      <tgroup cols="2">
       <thead>
	<row>
	 <entry>Server Character Set</entry>
	 <entry>Available Client Character Sets</entry>
	</row>
       </thead>
       <tbody>
	<row>
	 <entry><literal>SQL_ASCII</literal></entry>
	 <entry><literal>SQL_ASCII</literal>, <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>EUC_JP</literal></entry>
	 <entry><literal>EUC_JP</literal>, <literal>SJIS</literal>,
	 <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>EUC_CN</literal></entry>
	 <entry><literal>EUC_CN</literal>, <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>EUC_KR</literal></entry>
	 <entry><literal>EUC_KR</literal>, <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>JOHAB</literal></entry>
	 <entry><literal>JOHAB</literal>, <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>EUC_TW</literal></entry>
	 <entry><literal>EUC_TW</literal>, <literal>BIG5</literal>,
	 <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN1</literal></entry>
	 <entry><literal>LATIN1</literal>, <literal>UNICODE</literal>
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN2</literal></entry>
	 <entry><literal>LATIN2</literal>, <literal>WIN1250</literal>,
	 <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN3</literal></entry>
	 <entry><literal>LATIN3</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN4</literal></entry>
	 <entry><literal>LATIN4</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN5</literal></entry>
	 <entry><literal>LATIN5</literal>, <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN6</literal></entry>
	 <entry><literal>LATIN6</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN7</literal></entry>
	 <entry><literal>LATIN7</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN8</literal></entry>
	 <entry><literal>LATIN8</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN9</literal></entry>
	 <entry><literal>LATIN9</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>  
	 <entry><literal>LATIN10</literal></entry>
	 <entry><literal>LATIN10</literal>, <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_5</literal></entry>
	 <entry><literal>ISO_8859_5</literal>,
	 <literal>UNICODE</literal>,
	 <literal>MULE_INTERNAL</literal>,
	 <literal>WIN</literal>,
	 <literal>ALT</literal>,
	 <literal>KOI8</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_6</literal></entry>
	 <entry><literal>ISO_8859_6</literal>,
	 <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_7</literal></entry>
	 <entry><literal>ISO_8859_7</literal>,
	 <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>ISO_8859_8</literal></entry>
	 <entry><literal>ISO_8859_8</literal>,
	 <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>UNICODE</literal></entry>
	 <entry>
	 <literal>EUC_JP</literal>, <literal>SJIS</literal>, 
	 <literal>EUC_KR</literal>, <literal>UHC</literal>, <literal>JOHAB</literal>,
	 <literal>EUC_CN</literal>, <literal>GBK</literal>,
	 <literal>EUC_TW</literal>, <literal>BIG5</literal>, 
	 <literal>LATIN1</literal> to <literal>LATIN10</literal>, 
	 <literal>ISO_8859_5</literal>, 
	 <literal>ISO_8859_6</literal>,
 	 <literal>ISO_8859_7</literal>, 
	 <literal>ISO_8859_8</literal>, 
	 <literal>WIN</literal>, <literal>ALT</literal>, 
	 <literal>KOI8</literal>, 
	 <literal>WIN1256</literal>,
	 <literal>TCVN</literal>,
	 <literal>WIN874</literal>,
	 <literal>GB18030</literal>,
	 <literal>WIN1250</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>MULE_INTERNAL</literal></entry>
	 <entry><literal>EUC_JP</literal>, <literal>SJIS</literal>, <literal>EUC_KR</literal>, <literal>EUC_CN</literal>, 
	  <literal>EUC_TW</literal>, <literal>BIG5</literal>, <literal>LATIN1</literal> to <literal>LATIN5</literal>, 
	  <literal>WIN</literal>, <literal>ALT</literal>,
	 <literal>WIN1250</literal>,
	  <literal>BIG5</literal>, <literal>ISO_8859_5</literal>, <literal>KOI8</literal></entry>
	</row>
	<row>
	 <entry><literal>KOI8</literal></entry>
	 <entry><literal>ISO_8859_5</literal>, <literal>WIN</literal>, 
	 <literal>ALT</literal>, <literal>KOI8</literal>,
	 <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>WIN</literal></entry>
	 <entry><literal>ISO_8859_5</literal>, <literal>WIN</literal>, 
	 <literal>ALT</literal>, <literal>KOI8</literal>,
	 <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>ALT</literal></entry>
	 <entry><literal>ISO_8859_5</literal>, <literal>WIN</literal>, 
	 <literal>ALT</literal>, <literal>KOI8</literal>,
	 <literal>UNICODE</literal>, <literal>MULE_INTERNAL</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>WIN1256</literal></entry>
	 <entry><literal>WIN1256</literal>,
	 <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>TCVN</literal></entry>
	 <entry><literal>TCVN</literal>,
	 <literal>UNICODE</literal>
	 </entry>
	</row>
	<row>
	 <entry><literal>WIN874</literal></entry>
	 <entry><literal>WIN874</literal>,
	 <literal>UNICODE</literal>
	 </entry>
	</row>
       </tbody>
      </tgroup>
     </table>

    <para>
     To enable the automatic character set conversion, you have to
     tell <productname>PostgreSQL</productname> the character set
     (encoding) you would like to use in the client. There are several
     ways to accomplish this:

     <itemizedlist>
      <listitem>
       <para>
	Using the <command>\encoding</command> command in
	<application>psql</application>.
	<command>\encoding</command> allows you to change client
	encoding on the fly. For
	example, to change the encoding to <literal>SJIS</literal>, type:

<programlisting>
\encoding SJIS
</programlisting>
       </para>
      </listitem>

      <listitem>
       <para>
	Using <application>libpq</> functions.
	<command>\encoding</command> actually calls
	<function>PQsetClientEncoding()</function> for its purpose.

<synopsis>
int PQsetClientEncoding(PGconn *<replaceable>conn</replaceable>, const char *<replaceable>encoding</replaceable>);
</synopsis>

	where <replaceable>conn</replaceable> is a connection to the server,
	and <replaceable>encoding</replaceable> is the encoding you
	want to use. If the function successfully sets the encoding, it returns 0,
	otherwise -1. The current encoding for this connection can be determined by
	using:

<synopsis>
int PQclientEncoding(const PGconn *<replaceable>conn</replaceable>);
</synopsis>

	Note that it returns the encoding ID, not a symbolic string
	such as <literal>EUC_JP</literal>. To convert an encoding ID to an encoding name, you
	can use:

<synopsis>
char *pg_encoding_to_char(int <replaceable>encoding_id</replaceable>);
</synopsis>
       </para>
      </listitem>

      <listitem>
       <para>
	Using <command>SET CLIENT_ENCODING TO</command>.

	Setting the client encoding can be done with this SQL command:

<programlisting>
SET CLIENT_ENCODING TO '<replaceable>value</>';
</programlisting>

	Also you can use the more standard SQL syntax <literal>SET NAMES</literal> for this purpose:

<programlisting>
SET NAMES '<replaceable>value</>';
</programlisting>

	To query the current client encoding:

<programlisting>
SHOW CLIENT_ENCODING;
</programlisting>

	To return to the default encoding:

<programlisting>
RESET CLIENT_ENCODING;
</programlisting>
       </para>
      </listitem>

      <listitem>
       <para>
	Using <envar>PGCLIENTENCODING</envar>.

	If environment variable <envar>PGCLIENTENCODING</envar> is defined
	in the client's environment, that client encoding is automatically
	selected when a connection to the server is made.  (This can subsequently
	be overridden using any of the other methods mentioned above.)
       </para>
      </listitem>

      <listitem>
      <para>
       Using the configuration variable <varname>client_encoding</varname>.

      If the <varname>client_encoding</> variable in <filename>postgresql.conf</> is set, that
      client encoding is automatically selected when a connection to the
      server is made.  (This can subsequently be overridden using any of the
      other methods mentioned above.)
       </para>
      </listitem>

     </itemizedlist>
    </para>

    <para>
     If the conversion of a particular character is not possible --
     suppose you chose <literal>EUC_JP</literal> for the server and
     <literal>LATIN1</literal> for the client, then some Japanese
     characters cannot be converted to <literal>LATIN1</literal> -- it
     is transformed to its hexadecimal byte values in parentheses,
     e.g., <literal>(826C)</literal>.
    </para>
   </sect2>

   <sect2>
    <title>Further Reading</title>

    <para>
     These are good sources to start learning about various kinds of encoding
     systems.

     <variablelist>
      <varlistentry>
       <term><ulink url="ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf"></ulink></term>

       <listitem>
        <para>
         Detailed explanations of <literal>EUC_JP</literal>,
         <literal>EUC_CN</literal>, <literal>EUC_KR</literal>,
         <literal>EUC_TW</literal> appear in section 3.2.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term><ulink url="http://www.unicode.org/"></ulink></term>

       <listitem>
        <para>
         The web site of the Unicode Consortium
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>RFC 2044</term>

       <listitem>
        <para>
	 <acronym>UTF</acronym>-8 is defined here.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </para>
   </sect2>

  </sect1>


 <sect1 id="recode">
  <title>Single-Byte Character Set Recoding</>

  <para>
   You can set up this feature with the <option>--enable-recode</> option
   to <filename>configure</>. This option was formerly described as
   <quote>Cyrillic recode support</> which doesn't express all its
   power. It can be used for <emphasis>any</> single-byte character
   set recoding.
  </para>

  <para>
   This method uses a file <filename>charset.conf</> file located in
   the data directory for configuration.  It's a typical
   configuration text file where spaces and newlines separate fields
   and records and <literal>#</> starts a comment.  Three key words with the
   following syntax are recognized here:
<synopsis>
BaseCharset <replaceable>server_charset</>
RecodeTable <replaceable>from_charset</> <replaceable>to_charset</> <replaceable>file_name</>
HostCharset <replaceable>host_spec</>    <replaceable>host_charset</>
</synopsis>
  </para>

  <para>
   <token>BaseCharset</> defines the character set of the database server.
   All character set names are only used for mapping inside of
   <filename>charset.conf</> so you can freely use typing-friendly
   names.
  </para>

  <para>
   <token>RecodeTable</> records specify conversion tables between
   server and client.  The file name is relative to the
   data directory.  The table file format is very
   simple. There are no key words, and character mappings are represented by a
   pair of decimal or hexadecimal (prefixed by <literal>0x</>) values on single
   lines:
<synopsis>
<replaceable>char_value</>   <replaceable>converted_char_value</>
</synopsis>
   In the <filename>src/data/</> directory in the source distribution you can find an
   example <filename>charset.conf</> and a few recoding tables.
  </para>

  <para>
   <token>HostCharset</> records define the client character set by IP
   address. You can use a single IP address, an IP mask range starting
   from the given address or an IP interval (e.g., <literal>127.0.0.1</>,
   <literal>192.168.1.100/24</>, <literal>192.168.1.20-192.168.1.40</>).
  </para>

  <para>
   The <filename>charset.conf</> file is always processed to the
   end, so you can easily specify exceptions from preceding rules.
  </para>

  <para>
   As this solution is based on the client's IP address there are
   obviously some restrictions as well. You cannot use different
   character sets on the same host at the same time. It is also
   inconvenient when you boot your client hosts into multiple
   operating systems.  Nevertheless, when these restrictions are not
   limiting and you do not need multibyte characters then it is a
   simple and effective solution.
  </para>
 </sect1>

</chapter>

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