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1258 lines
41 KiB
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1258 lines
41 KiB
Plaintext
<!-- $PostgreSQL: pgsql/doc/src/sgml/charset.sgml,v 2.78 2006/07/28 16:21:57 tgl Exp $ -->
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<chapter id="charset">
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<title>Localization</>
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<para>
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This chapter describes the available localization features from the
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point of view of the administrator.
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<productname>PostgreSQL</productname> supports localization with
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two approaches:
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<itemizedlist>
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<listitem>
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<para>
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Using the locale features of the operating system to provide
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locale-specific collation order, number formatting, translated
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messages, and other aspects.
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</para>
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</listitem>
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<listitem>
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<para>
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Providing a number of different character sets defined in the
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<productname>PostgreSQL</productname> server, including
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multiple-byte character sets, to support storing text in all
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kinds of languages, and providing character set translation between
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client and server.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<sect1 id="locale">
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<title>Locale Support</title>
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<indexterm zone="locale"><primary>locale</></>
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<para>
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<firstterm>Locale</> support refers to an application respecting
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cultural preferences regarding alphabets, sorting, number
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formatting, etc. <productname>PostgreSQL</> uses the standard ISO
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C and <acronym>POSIX</acronym> locale facilities provided by the server operating
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system. For additional information refer to the documentation of your
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system.
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</para>
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<sect2>
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<title>Overview</>
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<para>
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Locale support is automatically initialized when a database
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cluster is created using <command>initdb</command>.
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<command>initdb</command> will initialize the database cluster
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with the locale setting of its execution environment by default,
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so if your system is already set to use the locale that you want
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in your database cluster then there is nothing else you need to
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do. If you want to use a different locale (or you are not sure
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which locale your system is set to), you can instruct
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<command>initdb</command> exactly which locale to use by
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specifying the <option>--locale</option> option. For example:
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<screen>
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initdb --locale=sv_SE
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</screen>
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</para>
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<para>
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This example sets the locale to Swedish (<literal>sv</>) as spoken
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in Sweden (<literal>SE</>). Other possibilities might be
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<literal>en_US</> (U.S. English) and <literal>fr_CA</> (French
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Canadian). If more than one character set can be useful for a
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locale then the specifications look like this:
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<literal>cs_CZ.ISO8859-2</>. What locales are available under what
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names on your system depends on what was provided by the operating
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system vendor and what was installed. (On most systems, the command
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<literal>locale -a</> will provide a list of available locales.)
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</para>
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<para>
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Occasionally it is useful to mix rules from several locales, e.g.,
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use English collation rules but Spanish messages. To support that, a
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set of locale subcategories exist that control only a certain
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aspect of the localization rules:
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<informaltable>
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<tgroup cols="2">
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<tbody>
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<row>
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<entry><envar>LC_COLLATE</></>
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<entry>String sort order</>
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</row>
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<row>
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<entry><envar>LC_CTYPE</></>
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<entry>Character classification (What is a letter? Its upper-case equivalent?)</>
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</row>
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<row>
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<entry><envar>LC_MESSAGES</></>
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<entry>Language of messages</>
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</row>
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<row>
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<entry><envar>LC_MONETARY</></>
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<entry>Formatting of currency amounts</>
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</row>
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<row>
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<entry><envar>LC_NUMERIC</></>
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<entry>Formatting of numbers</>
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</row>
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<row>
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<entry><envar>LC_TIME</></>
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<entry>Formatting of dates and times</>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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The category names translate into names of
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<command>initdb</command> options to override the locale choice
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for a specific category. For instance, to set the locale to
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French Canadian, but use U.S. rules for formatting currency, use
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<literal>initdb --locale=fr_CA --lc-monetary=en_US</literal>.
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</para>
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<para>
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If you want the system to behave as if it had no locale support,
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use the special locale <literal>C</> or <literal>POSIX</>.
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</para>
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<para>
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The nature of some locale categories is that their value has to be
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fixed for the lifetime of a database cluster. That is, once
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<command>initdb</command> has run, you cannot change them anymore.
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<literal>LC_COLLATE</literal> and <literal>LC_CTYPE</literal> are
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those categories. They affect the sort order of indexes, so they
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must be kept fixed, or indexes on text columns will become corrupt.
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<productname>PostgreSQL</productname> enforces this by recording
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the values of <envar>LC_COLLATE</> and <envar>LC_CTYPE</> that are
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seen by <command>initdb</>. The server automatically adopts
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those two values when it is started.
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</para>
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<para>
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The other locale categories can be changed as desired whenever the
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server is running by setting the run-time configuration variables
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that have the same name as the locale categories (see <xref
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linkend="runtime-config-client-format"> for details). The defaults that are
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chosen by <command>initdb</command> are actually only written into
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the configuration file <filename>postgresql.conf</filename> to
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serve as defaults when the server is started. If you delete these
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assignments from <filename>postgresql.conf</filename> then the
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server will inherit the settings from its execution environment.
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</para>
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<para>
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Note that the locale behavior of the server is determined by the
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environment variables seen by the server, not by the environment
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of any client. Therefore, be careful to configure the correct locale settings
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before starting the server. A consequence of this is that if
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client and server are set up in different locales, messages may
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appear in different languages depending on where they originated.
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</para>
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<note>
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<para>
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When we speak of inheriting the locale from the execution
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environment, this means the following on most operating systems:
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For a given locale category, say the collation, the following
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environment variables are consulted in this order until one is
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found to be set: <envar>LC_ALL</envar>, <envar>LC_COLLATE</envar>
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(the variable corresponding to the respective category),
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<envar>LANG</envar>. If none of these environment variables are
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set then the locale defaults to <literal>C</literal>.
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</para>
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<para>
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Some message localization libraries also look at the environment
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variable <envar>LANGUAGE</envar> which overrides all other locale
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settings for the purpose of setting the language of messages. If
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in doubt, please refer to the documentation of your operating
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system, in particular the documentation about
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<application>gettext</>, for more information.
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</para>
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</note>
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<para>
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To enable messages to be translated to the user's preferred language,
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<acronym>NLS</acronym> must have been enabled at build time. This
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choice is independent of the other locale support.
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</para>
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</sect2>
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<sect2>
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<title>Behavior</>
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<para>
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The locale settings influence the following SQL features:
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<itemizedlist>
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<listitem>
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<para>
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Sort order in queries using <literal>ORDER BY</> on textual data
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<indexterm><primary>ORDER BY</><secondary>and locales</></indexterm>
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</para>
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</listitem>
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<listitem>
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<para>
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The ability to use indexes with <literal>LIKE</> clauses
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<indexterm><primary>LIKE</><secondary>and locales</></indexterm>
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</para>
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</listitem>
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<listitem>
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<para>
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The <function>upper</>, <function>lower</>, and <function>initcap</>
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functions
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<indexterm><primary>upper</><secondary>and locales</></indexterm>
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<indexterm><primary>lower</><secondary>and locales</></indexterm>
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</para>
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</listitem>
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<listitem>
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<para>
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The <function>to_char</> family of functions
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<indexterm><primary>to_char</><secondary>and locales</></indexterm>
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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The drawback of using locales other than <literal>C</> or
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<literal>POSIX</> in <productname>PostgreSQL</> is its performance
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impact. It slows character handling and prevents ordinary indexes
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from being used by <literal>LIKE</>. For this reason use locales
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only if you actually need them.
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</para>
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<para>
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As a workaround to allow <productname>PostgreSQL</> to use indexes
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with <literal>LIKE</> clauses under a non-C locale, several custom
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operator classes exist. These allow the creation of an index that
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performs a strict character-by-character comparison, ignoring
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locale comparison rules. Refer to <xref linkend="indexes-opclass">
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for more information.
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</para>
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</sect2>
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<sect2>
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<title>Problems</>
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<para>
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If locale support doesn't work in spite of the explanation above,
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check that the locale support in your operating system is
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correctly configured. To check what locales are installed on your
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system, you may use the command <literal>locale -a</literal> if
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your operating system provides it.
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</para>
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<para>
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Check that <productname>PostgreSQL</> is actually using the locale
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that you think it is. <envar>LC_COLLATE</> and <envar>LC_CTYPE</>
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settings are determined at <command>initdb</> time and cannot be
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changed without repeating <command>initdb</>. Other locale
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settings including <envar>LC_MESSAGES</> and <envar>LC_MONETARY</>
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are initially determined by the environment the server is started
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in, but can be changed on-the-fly. You can check the active locale
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settings using the <command>SHOW</> command.
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</para>
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<para>
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The directory <filename>src/test/locale</> in the source
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distribution contains a test suite for
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<productname>PostgreSQL</>'s locale support.
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</para>
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<para>
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Client applications that handle server-side errors by parsing the
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text of the error message will obviously have problems when the
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server's messages are in a different language. Authors of such
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applications are advised to make use of the error code scheme
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instead.
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</para>
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<para>
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Maintaining catalogs of message translations requires the on-going
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efforts of many volunteers that want to see
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<productname>PostgreSQL</> speak their preferred language well.
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If messages in your language are currently not available or not fully
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translated, your assistance would be appreciated. If you want to
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help, refer to <xref linkend="nls"> or write to the developers'
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mailing list.
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</para>
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</sect2>
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</sect1>
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<sect1 id="multibyte">
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<title>Character Set Support</title>
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<indexterm zone="multibyte"><primary>character set</></>
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<para>
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The character set support in <productname>PostgreSQL</productname>
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allows you to store text in a variety of character sets, including
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single-byte character sets such as the ISO 8859 series and
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multiple-byte character sets such as <acronym>EUC</> (Extended Unix
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Code), UTF-8, and Mule internal code. All supported character sets
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can be used transparently by clients, but a few are not supported
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for use within the server (that is, as a server-side encoding).
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The default character set is selected while
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initializing your <productname>PostgreSQL</productname> database
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cluster using <command>initdb</>. It can be overridden when you
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create a database, so you can have multiple
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databases each with a different character set.
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</para>
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<sect2 id="multibyte-charset-supported">
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<title>Supported Character Sets</title>
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<para>
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<xref linkend="charset-table"> shows the character sets available
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for use in <productname>PostgreSQL</productname>.
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</para>
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<table id="charset-table">
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<title><productname>PostgreSQL</productname> Character Sets</title>
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<tgroup cols="6">
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Description</entry>
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<entry>Language</entry>
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<entry>Server?</entry>
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<!--
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The Bytes/Char field is populated by looking at the values returned
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by pg_wchar_table.mblen function for each encoding.
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-->
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<entry>Bytes/Char</entry>
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<entry>Aliases</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>BIG5</literal></entry>
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<entry>Big Five</entry>
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<entry>Traditional Chinese</entry>
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<entry>No</entry>
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<entry>1-2</entry>
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<entry><literal>WIN950</>, <literal>Windows950</></entry>
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</row>
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<row>
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<entry><literal>EUC_CN</literal></entry>
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<entry>Extended UNIX Code-CN</entry>
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<entry>Simplified Chinese</entry>
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<entry>Yes</entry>
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<entry>1-3</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>EUC_JP</literal></entry>
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<entry>Extended UNIX Code-JP</entry>
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<entry>Japanese</entry>
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<entry>Yes</entry>
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<entry>1-3</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>EUC_KR</literal></entry>
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<entry>Extended UNIX Code-KR</entry>
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<entry>Korean</entry>
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<entry>Yes</entry>
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<entry>1-3</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>EUC_TW</literal></entry>
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<entry>Extended UNIX Code-TW</entry>
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<entry>Traditional Chinese, Taiwanese</entry>
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<entry>Yes</entry>
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<entry>1-3</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>GB18030</literal></entry>
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<entry>National Standard</entry>
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<entry>Chinese</entry>
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<entry>No</entry>
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<entry>1-2</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>GBK</literal></entry>
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<entry>Extended National Standard</entry>
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<entry>Simplified Chinese</entry>
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<entry>No</entry>
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<entry>1-2</entry>
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<entry><literal>WIN936</>, <literal>Windows936</></entry>
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</row>
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<row>
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<entry><literal>ISO_8859_5</literal></entry>
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<entry>ISO 8859-5, <acronym>ECMA</> 113</entry>
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<entry>Latin/Cyrillic</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>ISO_8859_6</literal></entry>
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<entry>ISO 8859-6, <acronym>ECMA</> 114</entry>
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<entry>Latin/Arabic</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>ISO_8859_7</literal></entry>
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<entry>ISO 8859-7, <acronym>ECMA</> 118</entry>
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<entry>Latin/Greek</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>ISO_8859_8</literal></entry>
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<entry>ISO 8859-8, <acronym>ECMA</> 121</entry>
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<entry>Latin/Hebrew</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>JOHAB</literal></entry>
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<entry><acronym>JOHAB</></entry>
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<entry>Korean (Hangul)</entry>
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<entry>Yes</entry>
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<entry>1-3</entry>
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<entry></entry>
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</row>
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<row>
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<entry><literal>KOI8</literal></entry>
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<entry><acronym>KOI</acronym>8-R(U)</entry>
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<entry>Cyrillic</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>KOI8R</></entry>
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</row>
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<row>
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<entry><literal>LATIN1</literal></entry>
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<entry>ISO 8859-1, <acronym>ECMA</> 94</entry>
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<entry>Western European</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>ISO88591</></entry>
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</row>
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<row>
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<entry><literal>LATIN2</literal></entry>
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<entry>ISO 8859-2, <acronym>ECMA</> 94</entry>
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<entry>Central European</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>ISO88592</></entry>
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</row>
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<row>
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<entry><literal>LATIN3</literal></entry>
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<entry>ISO 8859-3, <acronym>ECMA</> 94</entry>
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<entry>South European</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>ISO88593</></entry>
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</row>
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<row>
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<entry><literal>LATIN4</literal></entry>
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<entry>ISO 8859-4, <acronym>ECMA</> 94</entry>
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<entry>North European</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>ISO88594</></entry>
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</row>
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<row>
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<entry><literal>LATIN5</literal></entry>
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<entry>ISO 8859-9, <acronym>ECMA</> 128</entry>
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<entry>Turkish</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>ISO88599</></entry>
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</row>
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<row>
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<entry><literal>LATIN6</literal></entry>
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<entry>ISO 8859-10, <acronym>ECMA</> 144</entry>
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<entry>Nordic</entry>
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<entry>Yes</entry>
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<entry>1</entry>
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<entry><literal>ISO885910</></entry>
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</row>
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<row>
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<entry><literal>LATIN7</literal></entry>
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<entry>ISO 8859-13</entry>
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<entry>Baltic</entry>
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|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885913</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN8</literal></entry>
|
|
<entry>ISO 8859-14</entry>
|
|
<entry>Celtic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885914</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN9</literal></entry>
|
|
<entry>ISO 8859-15</entry>
|
|
<entry>LATIN1 with Euro and accents</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry>ISO885915</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN10</literal></entry>
|
|
<entry>ISO 8859-16, <acronym>ASRO</> SR 14111</entry>
|
|
<entry>Romanian</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885916</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>MULE_INTERNAL</literal></entry>
|
|
<entry>Mule internal code</entry>
|
|
<entry>Multilingual Emacs</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-4</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>SJIS</literal></entry>
|
|
<entry>Shift JIS</entry>
|
|
<entry>Japanese</entry>
|
|
<entry>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry><literal>Mskanji</>, <literal>ShiftJIS</>, <literal>WIN932</>, <literal>Windows932</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>SQL_ASCII</literal></entry>
|
|
<entry>unspecified (see text)</entry>
|
|
<entry><emphasis>any</></entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>UHC</literal></entry>
|
|
<entry>Unified Hangul Code</entry>
|
|
<entry>Korean</entry>
|
|
<entry>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry><literal>WIN949</>, <literal>Windows949</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>UTF8</literal></entry>
|
|
<entry>Unicode, 8-bit</entry>
|
|
<entry><emphasis>all</></entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-4</entry>
|
|
<entry><literal>Unicode</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN866</literal></entry>
|
|
<entry>Windows CP866</entry>
|
|
<entry>Cyrillic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ALT</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN874</literal></entry>
|
|
<entry>Windows CP874</entry>
|
|
<entry>Thai</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1250</literal></entry>
|
|
<entry>Windows CP1250</entry>
|
|
<entry>Central European</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1251</literal></entry>
|
|
<entry>Windows CP1251</entry>
|
|
<entry>Cyrillic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>WIN</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1252</literal></entry>
|
|
<entry>Windows CP1252</entry>
|
|
<entry>Western European</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1253</literal></entry>
|
|
<entry>Windows CP1253</entry>
|
|
<entry>Greek</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1254</literal></entry>
|
|
<entry>Windows CP1254</entry>
|
|
<entry>Turkish</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1255</literal></entry>
|
|
<entry>Windows CP1255</entry>
|
|
<entry>Hebrew</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1256</literal></entry>
|
|
<entry>Windows CP1256</entry>
|
|
<entry>Arabic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1257</literal></entry>
|
|
<entry>Windows CP1257</entry>
|
|
<entry>Baltic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1258</literal></entry>
|
|
<entry>Windows CP1258</entry>
|
|
<entry>Vietnamese</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ABC</>, <literal>TCVN</>, <literal>TCVN5712</>, <literal>VSCII</></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<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>
|
|
|
|
<para>
|
|
The <literal>SQL_ASCII</> setting behaves considerably differently
|
|
from the other settings. When the server character set is
|
|
<literal>SQL_ASCII</>, the server interprets byte values 0-127
|
|
according to the ASCII standard, while byte values 128-255 are taken
|
|
as uninterpreted characters. No encoding conversion will be done when
|
|
the setting is <literal>SQL_ASCII</>. Thus, this setting is not so
|
|
much a declaration that a specific encoding is in use, as a declaration
|
|
of ignorance about the encoding. In most cases, if you are
|
|
working with any non-ASCII data, it is unwise to use the
|
|
<literal>SQL_ASCII</> setting, because
|
|
<productname>PostgreSQL</productname> will be unable to help you by
|
|
converting or validating non-ASCII characters.
|
|
</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, <command>initdb</> attempts to determine the appropriate
|
|
encoding to use based on the specified or default locale.
|
|
</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
|
|
postgres | t-ishii | EUC_JP
|
|
regression | t-ishii | SQL_ASCII
|
|
template1 | t-ishii | EUC_JP
|
|
test | t-ishii | EUC_JP
|
|
utf8 | t-ishii | UTF8
|
|
(9 rows)
|
|
</screen>
|
|
</para>
|
|
|
|
<important>
|
|
<para>
|
|
Although you can specify any encoding you want for a database, it is
|
|
unwise to choose an encoding that is not what is expected by the locale
|
|
you have selected. The <literal>LC_COLLATE</literal> and
|
|
<literal>LC_CTYPE</literal> settings imply a particular encoding,
|
|
and locale-dependent operations (such as sorting) are likely to
|
|
misinterpret data that is in an incompatible encoding.
|
|
</para>
|
|
|
|
<para>
|
|
Since these locale settings are frozen by <command>initdb</>, the
|
|
apparent flexibility to use different encodings in different databases
|
|
of a cluster is more theoretical than real. It is likely that these
|
|
mechanisms will be revisited in future versions of
|
|
<productname>PostgreSQL</productname>.
|
|
</para>
|
|
|
|
<para>
|
|
One way to use multiple encodings safely is to set the locale to
|
|
<literal>C</> or <literal>POSIX</> during <command>initdb</>, thus
|
|
disabling any real locale awareness.
|
|
</para>
|
|
</important>
|
|
</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 set combinations. The conversion information is stored in the
|
|
<literal>pg_conversion</> system catalog. <productname>PostgreSQL</>
|
|
comes with some predefined conversions, as shown in <xref
|
|
linkend="multibyte-translation-table">. You can create a new
|
|
conversion using the SQL command <command>CREATE CONVERSION</command>.
|
|
</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>BIG5</literal></entry>
|
|
<entry><emphasis>not supported as a server encoding</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_CN</literal></entry>
|
|
<entry><emphasis>EUC_CN</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_JP</literal></entry>
|
|
<entry><emphasis>EUC_JP</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>SJIS</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_KR</literal></entry>
|
|
<entry><emphasis>EUC_KR</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_TW</literal></entry>
|
|
<entry><emphasis>EUC_TW</emphasis>,
|
|
<literal>BIG5</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>GB18030</literal></entry>
|
|
<entry><emphasis>not supported as a server encoding</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>GBK</literal></entry>
|
|
<entry><emphasis>not supported as a server encoding</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_5</literal></entry>
|
|
<entry><emphasis>ISO_8859_5</emphasis>,
|
|
<literal>KOI8</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>,
|
|
<literal>WIN866</literal>,
|
|
<literal>WIN1251</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_6</literal></entry>
|
|
<entry><emphasis>ISO_8859_6</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_7</literal></entry>
|
|
<entry><emphasis>ISO_8859_7</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_8</literal></entry>
|
|
<entry><emphasis>ISO_8859_8</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>JOHAB</literal></entry>
|
|
<entry><emphasis>JOHAB</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>KOI8</literal></entry>
|
|
<entry><emphasis>KOI8</emphasis>,
|
|
<literal>ISO_8859_5</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>,
|
|
<literal>WIN866</literal>,
|
|
<literal>WIN1251</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN1</literal></entry>
|
|
<entry><emphasis>LATIN1</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN2</literal></entry>
|
|
<entry><emphasis>LATIN2</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>,
|
|
<literal>WIN1250</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN3</literal></entry>
|
|
<entry><emphasis>LATIN3</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN4</literal></entry>
|
|
<entry><emphasis>LATIN4</emphasis>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN5</literal></entry>
|
|
<entry><emphasis>LATIN5</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN6</literal></entry>
|
|
<entry><emphasis>LATIN6</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN7</literal></entry>
|
|
<entry><emphasis>LATIN7</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN8</literal></entry>
|
|
<entry><emphasis>LATIN8</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN9</literal></entry>
|
|
<entry><emphasis>LATIN9</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN10</literal></entry>
|
|
<entry><emphasis>LATIN10</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>MULE_INTERNAL</literal></entry>
|
|
<entry><emphasis>MULE_INTERNAL</emphasis>,
|
|
<literal>BIG5</literal>,
|
|
<literal>EUC_CN</literal>,
|
|
<literal>EUC_JP</literal>,
|
|
<literal>EUC_KR</literal>,
|
|
<literal>EUC_TW</literal>,
|
|
<literal>ISO_8859_5</literal>,
|
|
<literal>KOI8</literal>,
|
|
<literal>LATIN1</literal> to <literal>LATIN4</literal>,
|
|
<literal>SJIS</literal>,
|
|
<literal>WIN866</literal>,
|
|
<literal>WIN1250</literal>,
|
|
<literal>WIN1251</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>SJIS</literal></entry>
|
|
<entry><emphasis>not supported as a server encoding</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>SQL_ASCII</literal></entry>
|
|
<entry><emphasis>any (no conversion will be performed)</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>UHC</literal></entry>
|
|
<entry><emphasis>not supported as a server encoding</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>UTF8</literal></entry>
|
|
<entry><emphasis>all supported encodings</emphasis>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN866</literal></entry>
|
|
<entry><emphasis>WIN866</emphasis>,
|
|
<literal>ISO_8859_5</literal>,
|
|
<literal>KOI8</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>,
|
|
<literal>WIN1251</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN874</literal></entry>
|
|
<entry><emphasis>WIN874</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1250</literal></entry>
|
|
<entry><emphasis>WIN1250</emphasis>,
|
|
<literal>LATIN2</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1251</literal></entry>
|
|
<entry><emphasis>WIN1251</emphasis>,
|
|
<literal>ISO_8859_5</literal>,
|
|
<literal>KOI8</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>,
|
|
<literal>WIN866</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1252</literal></entry>
|
|
<entry><emphasis>WIN1252</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1253</literal></entry>
|
|
<entry><emphasis>WIN1253</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1254</literal></entry>
|
|
<entry><emphasis>WIN1254</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1255</literal></entry>
|
|
<entry><emphasis>WIN1255</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1256</literal></entry>
|
|
<entry><emphasis>WIN1256</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1257</literal></entry>
|
|
<entry><emphasis>WIN1257</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1258</literal></entry>
|
|
<entry><emphasis>WIN1258</emphasis>,
|
|
<literal>UTF8</literal>
|
|
</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>
|
|
To enable 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 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 the 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 <xref
|
|
linkend="guc-client-encoding">. If the
|
|
<varname>client_encoding</> variable 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 do not have a representation in
|
|
<literal>LATIN1</literal> — then an error is reported.
|
|
</para>
|
|
|
|
<para>
|
|
If the client character set is defined as <literal>SQL_ASCII</>,
|
|
encoding conversion is disabled, regardless of the server's character
|
|
set. Just as for the server, use of <literal>SQL_ASCII</> is unwise
|
|
unless you are working with all-ASCII data.
|
|
</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="http://www.i18ngurus.com/docs/984813247.html"></ulink></term>
|
|
|
|
<listitem>
|
|
<para>
|
|
An extensive collection of documents about character sets, encodings,
|
|
and code pages.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<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>
|
|
|
|
</chapter>
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
Local variables:
|
|
mode:sgml
|
|
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|
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sgml-shorttag:t
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|
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|
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|
|
sgml-indent-data:t
|
|
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|
|
sgml-default-dtd-file:"./reference.ced"
|
|
sgml-exposed-tags:nil
|
|
sgml-local-catalogs:("/usr/lib/sgml/catalog")
|
|
sgml-local-ecat-files:nil
|
|
End:
|
|
-->
|