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Since some preparation work had already been done, the only source changes left were changing empty-element tags like <xref linkend="foo"> to <xref linkend="foo"/>, and changing the DOCTYPE. The source files are still named *.sgml, but they are actually XML files now. Renaming could be considered later. In the build system, the intermediate step to convert from SGML to XML is removed. Everything is build straight from the source files again. The OpenSP (or the old SP) package is no longer needed. The documentation toolchain instructions are updated and are much simpler now. Peter Eisentraut, Alexander Lakhin, Jürgen Purtz
1889 lines
68 KiB
Plaintext
1889 lines
68 KiB
Plaintext
<!-- doc/src/sgml/charset.sgml -->
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<chapter id="charset">
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<title>Localization</title>
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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 two localization
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facilities:
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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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This is covered in <xref linkend="locale"/> and
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<xref linkend="collation"/>.
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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 to support storing text
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in all kinds of languages, and providing character set translation
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between client and server.
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This is covered in <xref linkend="multibyte"/>.
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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</primary></indexterm>
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<para>
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<firstterm>Locale</firstterm> support refers to an application respecting
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cultural preferences regarding alphabets, sorting, number
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formatting, etc. <productname>PostgreSQL</productname> 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</title>
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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 for Unix systems sets the locale to Swedish
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(<literal>sv</literal>) as spoken
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in Sweden (<literal>SE</literal>). Other possibilities might include
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<literal>en_US</literal> (U.S. English) and <literal>fr_CA</literal> (French
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Canadian). If more than one character set can be used for a
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locale then the specifications can take the form
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<replaceable>language_territory.codeset</replaceable>. For example,
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<literal>fr_BE.UTF-8</literal> represents the French language (fr) as
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spoken in Belgium (BE), with a <acronym>UTF-8</acronym> character set
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encoding.
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</para>
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<para>
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What locales are available on your
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system under what names depends on what was provided by the operating
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system vendor and what was installed. On most Unix systems, the command
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<literal>locale -a</literal> will provide a list of available locales.
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Windows uses more verbose locale names, such as <literal>German_Germany</literal>
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or <literal>Swedish_Sweden.1252</literal>, but the principles are the same.
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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 certain
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aspects 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</envar></entry>
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<entry>String sort order</entry>
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</row>
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<row>
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<entry><envar>LC_CTYPE</envar></entry>
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<entry>Character classification (What is a letter? Its upper-case equivalent?)</entry>
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</row>
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<row>
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<entry><envar>LC_MESSAGES</envar></entry>
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<entry>Language of messages</entry>
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</row>
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<row>
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<entry><envar>LC_MONETARY</envar></entry>
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<entry>Formatting of currency amounts</entry>
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</row>
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<row>
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<entry><envar>LC_NUMERIC</envar></entry>
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<entry>Formatting of numbers</entry>
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</row>
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<row>
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<entry><envar>LC_TIME</envar></entry>
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<entry>Formatting of dates and times</entry>
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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 name <literal>C</literal>, or equivalently
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<literal>POSIX</literal>.
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</para>
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<para>
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Some locale categories must have their values
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fixed when the database is created. You can use different settings
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for different databases, but once a database is created, you cannot
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change them for that database anymore. <literal>LC_COLLATE</literal>
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and <literal>LC_CTYPE</literal> are these categories. They affect
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the sort order of indexes, so they must be kept fixed, or indexes on
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text columns would become corrupt.
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(But you can alleviate this restriction using collations, as discussed
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in <xref linkend="collation"/>.)
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The default values for these
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categories are determined when <command>initdb</command> is run, and
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those values are used when new databases are created, unless
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specified otherwise in the <command>CREATE DATABASE</command> command.
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</para>
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<para>
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The other locale categories can be changed whenever desired
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by setting the server configuration parameters
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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 values
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that are chosen by <command>initdb</command> are actually only written
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into the configuration file <filename>postgresql.conf</filename> to
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serve as defaults when the server is started. If you remove 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 might
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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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(or 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</application>.
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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 selected at build time
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(<literal>configure --enable-nls</literal>). All other locale support is
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built in automatically.
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</para>
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</sect2>
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<sect2>
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<title>Behavior</title>
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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</literal> or the standard
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comparison operators on textual data
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<indexterm><primary>ORDER BY</primary><secondary>and locales</secondary></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>, <function>lower</function>, and <function>initcap</function>
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functions
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<indexterm><primary>upper</primary><secondary>and locales</secondary></indexterm>
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<indexterm><primary>lower</primary><secondary>and locales</secondary></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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Pattern matching operators (<literal>LIKE</literal>, <literal>SIMILAR TO</literal>,
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and POSIX-style regular expressions); locales affect both case
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insensitive matching and the classification of characters by
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character-class regular expressions
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<indexterm><primary>LIKE</primary><secondary>and locales</secondary></indexterm>
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<indexterm><primary>regular expressions</primary><secondary>and locales</secondary></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</function> family of functions
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<indexterm><primary>to_char</primary><secondary>and locales</secondary></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</literal> clauses
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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</literal> or
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<literal>POSIX</literal> in <productname>PostgreSQL</productname> 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</literal>. 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</productname> to use indexes
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with <literal>LIKE</literal> 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. Another approach is to create indexes using
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the <literal>C</literal> collation, as discussed in
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<xref linkend="collation"/>.
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</para>
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</sect2>
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<sect2>
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<title>Problems</title>
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<para>
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If locale support doesn't work according to 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 can 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</productname> is actually using the locale
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that you think it is. The <envar>LC_COLLATE</envar> and <envar>LC_CTYPE</envar>
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settings are determined when a database is created, and cannot be
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changed except by creating a new database. Other locale
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settings including <envar>LC_MESSAGES</envar> and <envar>LC_MONETARY</envar>
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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> command.
|
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</para>
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<para>
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The directory <filename>src/test/locale</filename> in the source
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distribution contains a test suite for
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<productname>PostgreSQL</productname>'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</productname> 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="collation">
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<title>Collation Support</title>
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<indexterm zone="collation"><primary>collation</primary></indexterm>
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<para>
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The collation feature allows specifying the sort order and character
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classification behavior of data per-column, or even per-operation.
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This alleviates the restriction that the
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<symbol>LC_COLLATE</symbol> and <symbol>LC_CTYPE</symbol> settings
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of a database cannot be changed after its creation.
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</para>
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<sect2>
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<title>Concepts</title>
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<para>
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Conceptually, every expression of a collatable data type has a
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collation. (The built-in collatable data types are
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<type>text</type>, <type>varchar</type>, and <type>char</type>.
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User-defined base types can also be marked collatable, and of course
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a domain over a collatable data type is collatable.) If the
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expression is a column reference, the collation of the expression is the
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defined collation of the column. If the expression is a constant, the
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collation is the default collation of the data type of the
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constant. The collation of a more complex expression is derived
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from the collations of its inputs, as described below.
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</para>
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<para>
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The collation of an expression can be the <quote>default</quote>
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collation, which means the locale settings defined for the
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database. It is also possible for an expression's collation to be
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indeterminate. In such cases, ordering operations and other
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operations that need to know the collation will fail.
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</para>
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<para>
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When the database system has to perform an ordering or a character
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classification, it uses the collation of the input expression. This
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happens, for example, with <literal>ORDER BY</literal> clauses
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and function or operator calls such as <literal><</literal>.
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The collation to apply for an <literal>ORDER BY</literal> clause
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is simply the collation of the sort key. The collation to apply for a
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function or operator call is derived from the arguments, as described
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below. In addition to comparison operators, collations are taken into
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account by functions that convert between lower and upper case
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letters, such as <function>lower</function>, <function>upper</function>, and
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<function>initcap</function>; by pattern matching operators; and by
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<function>to_char</function> and related functions.
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</para>
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<para>
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For a function or operator call, the collation that is derived by
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examining the argument collations is used at run time for performing
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the specified operation. If the result of the function or operator
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call is of a collatable data type, the collation is also used at parse
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time as the defined collation of the function or operator expression,
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in case there is a surrounding expression that requires knowledge of
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its collation.
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</para>
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<para>
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The <firstterm>collation derivation</firstterm> of an expression can be
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implicit or explicit. This distinction affects how collations are
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combined when multiple different collations appear in an
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expression. An explicit collation derivation occurs when a
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<literal>COLLATE</literal> clause is used; all other collation
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derivations are implicit. When multiple collations need to be
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combined, for example in a function call, the following rules are
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used:
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<orderedlist>
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<listitem>
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<para>
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If any input expression has an explicit collation derivation, then
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all explicitly derived collations among the input expressions must be
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the same, otherwise an error is raised. If any explicitly
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derived collation is present, that is the result of the
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collation combination.
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</para>
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</listitem>
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<listitem>
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<para>
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Otherwise, all input expressions must have the same implicit
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collation derivation or the default collation. If any non-default
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collation is present, that is the result of the collation combination.
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Otherwise, the result is the default collation.
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</para>
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</listitem>
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<listitem>
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<para>
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If there are conflicting non-default implicit collations among the
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input expressions, then the combination is deemed to have indeterminate
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collation. This is not an error condition unless the particular
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function being invoked requires knowledge of the collation it should
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apply. If it does, an error will be raised at run-time.
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</para>
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</listitem>
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</orderedlist>
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For example, consider this table definition:
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<programlisting>
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CREATE TABLE test1 (
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a text COLLATE "de_DE",
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b text COLLATE "es_ES",
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...
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);
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</programlisting>
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Then in
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<programlisting>
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SELECT a < 'foo' FROM test1;
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</programlisting>
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the <literal><</literal> comparison is performed according to
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<literal>de_DE</literal> rules, because the expression combines an
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implicitly derived collation with the default collation. But in
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<programlisting>
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SELECT a < ('foo' COLLATE "fr_FR") FROM test1;
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</programlisting>
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the comparison is performed using <literal>fr_FR</literal> rules,
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because the explicit collation derivation overrides the implicit one.
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Furthermore, given
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<programlisting>
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SELECT a < b FROM test1;
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</programlisting>
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the parser cannot determine which collation to apply, since the
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<structfield>a</structfield> and <structfield>b</structfield> columns have conflicting
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implicit collations. Since the <literal><</literal> operator
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|
does need to know which collation to use, this will result in an
|
|
error. The error can be resolved by attaching an explicit collation
|
|
specifier to either input expression, thus:
|
|
<programlisting>
|
|
SELECT a < b COLLATE "de_DE" FROM test1;
|
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</programlisting>
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|
or equivalently
|
|
<programlisting>
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|
SELECT a COLLATE "de_DE" < b FROM test1;
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</programlisting>
|
|
On the other hand, the structurally similar case
|
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<programlisting>
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SELECT a || b FROM test1;
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</programlisting>
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does not result in an error, because the <literal>||</literal> operator
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does not care about collations: its result is the same regardless
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of the collation.
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</para>
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<para>
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|
The collation assigned to a function or operator's combined input
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|
expressions is also considered to apply to the function or operator's
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|
result, if the function or operator delivers a result of a collatable
|
|
data type. So, in
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<programlisting>
|
|
SELECT * FROM test1 ORDER BY a || 'foo';
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|
</programlisting>
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|
the ordering will be done according to <literal>de_DE</literal> rules.
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|
But this query:
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<programlisting>
|
|
SELECT * FROM test1 ORDER BY a || b;
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|
</programlisting>
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|
results in an error, because even though the <literal>||</literal> operator
|
|
doesn't need to know a collation, the <literal>ORDER BY</literal> clause does.
|
|
As before, the conflict can be resolved with an explicit collation
|
|
specifier:
|
|
<programlisting>
|
|
SELECT * FROM test1 ORDER BY a || b COLLATE "fr_FR";
|
|
</programlisting>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="collation-managing">
|
|
<title>Managing Collations</title>
|
|
|
|
<para>
|
|
A collation is an SQL schema object that maps an SQL name to locales
|
|
provided by libraries installed in the operating system. A collation
|
|
definition has a <firstterm>provider</firstterm> that specifies which
|
|
library supplies the locale data. One standard provider name
|
|
is <literal>libc</literal>, which uses the locales provided by the
|
|
operating system C library. These are the locales that most tools
|
|
provided by the operating system use. Another provider
|
|
is <literal>icu</literal>, which uses the external
|
|
ICU<indexterm><primary>ICU</primary></indexterm> library. ICU locales can only be
|
|
used if support for ICU was configured when PostgreSQL was built.
|
|
</para>
|
|
|
|
<para>
|
|
A collation object provided by <literal>libc</literal> maps to a
|
|
combination of <symbol>LC_COLLATE</symbol> and <symbol>LC_CTYPE</symbol>
|
|
settings, as accepted by the <literal>setlocale()</literal> system library call. (As
|
|
the name would suggest, the main purpose of a collation is to set
|
|
<symbol>LC_COLLATE</symbol>, which controls the sort order. But
|
|
it is rarely necessary in practice to have an
|
|
<symbol>LC_CTYPE</symbol> setting that is different from
|
|
<symbol>LC_COLLATE</symbol>, so it is more convenient to collect
|
|
these under one concept than to create another infrastructure for
|
|
setting <symbol>LC_CTYPE</symbol> per expression.) Also,
|
|
a <literal>libc</literal> collation
|
|
is tied to a character set encoding (see <xref linkend="multibyte"/>).
|
|
The same collation name may exist for different encodings.
|
|
</para>
|
|
|
|
<para>
|
|
A collation object provided by <literal>icu</literal> maps to a named
|
|
collator provided by the ICU library. ICU does not support
|
|
separate <quote>collate</quote> and <quote>ctype</quote> settings, so
|
|
they are always the same. Also, ICU collations are independent of the
|
|
encoding, so there is always only one ICU collation of a given name in
|
|
a database.
|
|
</para>
|
|
|
|
<sect3>
|
|
<title>Standard Collations</title>
|
|
|
|
<para>
|
|
On all platforms, the collations named <literal>default</literal>,
|
|
<literal>C</literal>, and <literal>POSIX</literal> are available. Additional
|
|
collations may be available depending on operating system support.
|
|
The <literal>default</literal> collation selects the <symbol>LC_COLLATE</symbol>
|
|
and <symbol>LC_CTYPE</symbol> values specified at database creation time.
|
|
The <literal>C</literal> and <literal>POSIX</literal> collations both specify
|
|
<quote>traditional C</quote> behavior, in which only the ASCII letters
|
|
<quote><literal>A</literal></quote> through <quote><literal>Z</literal></quote>
|
|
are treated as letters, and sorting is done strictly by character
|
|
code byte values.
|
|
</para>
|
|
|
|
<para>
|
|
Additionally, the SQL standard collation name <literal>ucs_basic</literal>
|
|
is available for encoding <literal>UTF8</literal>. It is equivalent
|
|
to <literal>C</literal> and sorts by Unicode code point.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3>
|
|
<title>Predefined Collations</title>
|
|
|
|
<para>
|
|
If the operating system provides support for using multiple locales
|
|
within a single program (<function>newlocale</function> and related functions),
|
|
or if support for ICU is configured,
|
|
then when a database cluster is initialized, <command>initdb</command>
|
|
populates the system catalog <literal>pg_collation</literal> with
|
|
collations based on all the locales it finds in the operating
|
|
system at the time.
|
|
</para>
|
|
|
|
<para>
|
|
To inspect the currently available locales, use the query <literal>SELECT
|
|
* FROM pg_collation</literal>, or the command <command>\dOS+</command>
|
|
in <application>psql</application>.
|
|
</para>
|
|
|
|
<sect4>
|
|
<title>libc collations</title>
|
|
|
|
<para>
|
|
For example, the operating system might
|
|
provide a locale named <literal>de_DE.utf8</literal>.
|
|
<command>initdb</command> would then create a collation named
|
|
<literal>de_DE.utf8</literal> for encoding <literal>UTF8</literal>
|
|
that has both <symbol>LC_COLLATE</symbol> and
|
|
<symbol>LC_CTYPE</symbol> set to <literal>de_DE.utf8</literal>.
|
|
It will also create a collation with the <literal>.utf8</literal>
|
|
tag stripped off the name. So you could also use the collation
|
|
under the name <literal>de_DE</literal>, which is less cumbersome
|
|
to write and makes the name less encoding-dependent. Note that,
|
|
nevertheless, the initial set of collation names is
|
|
platform-dependent.
|
|
</para>
|
|
|
|
<para>
|
|
The default set of collations provided by <literal>libc</literal> map
|
|
directly to the locales installed in the operating system, which can be
|
|
listed using the command <literal>locale -a</literal>. In case
|
|
a <literal>libc</literal> collation is needed that has different values
|
|
for <symbol>LC_COLLATE</symbol> and <symbol>LC_CTYPE</symbol>, or if new
|
|
locales are installed in the operating system after the database system
|
|
was initialized, then a new collation may be created using
|
|
the <xref linkend="sql-createcollation"/> command.
|
|
New operating system locales can also be imported en masse using
|
|
the <link linkend="functions-admin-collation"><function>pg_import_system_collations()</function></link> function.
|
|
</para>
|
|
|
|
<para>
|
|
Within any particular database, only collations that use that
|
|
database's encoding are of interest. Other entries in
|
|
<literal>pg_collation</literal> are ignored. Thus, a stripped collation
|
|
name such as <literal>de_DE</literal> can be considered unique
|
|
within a given database even though it would not be unique globally.
|
|
Use of the stripped collation names is recommended, since it will
|
|
make one less thing you need to change if you decide to change to
|
|
another database encoding. Note however that the <literal>default</literal>,
|
|
<literal>C</literal>, and <literal>POSIX</literal> collations can be used regardless of
|
|
the database encoding.
|
|
</para>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</productname> considers distinct collation
|
|
objects to be incompatible even when they have identical properties.
|
|
Thus for example,
|
|
<programlisting>
|
|
SELECT a COLLATE "C" < b COLLATE "POSIX" FROM test1;
|
|
</programlisting>
|
|
will draw an error even though the <literal>C</literal> and <literal>POSIX</literal>
|
|
collations have identical behaviors. Mixing stripped and non-stripped
|
|
collation names is therefore not recommended.
|
|
</para>
|
|
</sect4>
|
|
|
|
<sect4>
|
|
<title>ICU collations</title>
|
|
|
|
<para>
|
|
With ICU, it is not sensible to enumerate all possible locale names. ICU
|
|
uses a particular naming system for locales, but there are many more ways
|
|
to name a locale than there are actually distinct locales.
|
|
<command>initdb</command> uses the ICU APIs to extract a set of distinct
|
|
locales to populate the initial set of collations. Collations provided by
|
|
ICU are created in the SQL environment with names in BCP 47 language tag
|
|
format, with a <quote>private use</quote>
|
|
extension <literal>-x-icu</literal> appended, to distinguish them from
|
|
libc locales.
|
|
</para>
|
|
|
|
<para>
|
|
Here are some example collations that might be created:
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>de-x-icu</literal></term>
|
|
<listitem>
|
|
<para>German collation, default variant</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>de-AT-x-icu</literal></term>
|
|
<listitem>
|
|
<para>German collation for Austria, default variant</para>
|
|
<para>
|
|
(There are also, say, <literal>de-DE-x-icu</literal>
|
|
or <literal>de-CH-x-icu</literal>, but as of this writing, they are
|
|
equivalent to <literal>de-x-icu</literal>.)
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>und-x-icu</literal> (for <quote>undefined</quote>)</term>
|
|
<listitem>
|
|
<para>
|
|
ICU <quote>root</quote> collation. Use this to get a reasonable
|
|
language-agnostic sort order.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
|
|
<para>
|
|
Some (less frequently used) encodings are not supported by ICU. When the
|
|
database encoding is one of these, ICU collation entries
|
|
in <literal>pg_collation</literal> are ignored. Attempting to use one
|
|
will draw an error along the lines of <quote>collation "de-x-icu" for
|
|
encoding "WIN874" does not exist</quote>.
|
|
</para>
|
|
</sect4>
|
|
</sect3>
|
|
|
|
<sect3 id="collation-create">
|
|
<title>Creating New Collation Objects</title>
|
|
|
|
<para>
|
|
If the standard and predefined collations are not sufficient, users can
|
|
create their own collation objects using the SQL
|
|
command <xref linkend="sql-createcollation"/>.
|
|
</para>
|
|
|
|
<para>
|
|
The standard and predefined collations are in the
|
|
schema <literal>pg_catalog</literal>, like all predefined objects.
|
|
User-defined collations should be created in user schemas. This also
|
|
ensures that they are saved by <command>pg_dump</command>.
|
|
</para>
|
|
|
|
<sect4>
|
|
<title>libc collations</title>
|
|
|
|
<para>
|
|
New libc collations can be created like this:
|
|
<programlisting>
|
|
CREATE COLLATION german (provider = libc, locale = 'de_DE');
|
|
</programlisting>
|
|
The exact values that are acceptable for the <literal>locale</literal>
|
|
clause in this command depend on the operating system. On Unix-like
|
|
systems, the command <literal>locale -a</literal> will show a list.
|
|
</para>
|
|
|
|
<para>
|
|
Since the predefined libc collations already include all collations
|
|
defined in the operating system when the database instance is
|
|
initialized, it is not often necessary to manually create new ones.
|
|
Reasons might be if a different naming system is desired (in which case
|
|
see also <xref linkend="collation-copy"/>) or if the operating system has
|
|
been upgraded to provide new locale definitions (in which case see
|
|
also <link linkend="functions-admin-collation"><function>pg_import_system_collations()</function></link>).
|
|
</para>
|
|
</sect4>
|
|
|
|
<sect4>
|
|
<title>ICU collations</title>
|
|
|
|
<para>
|
|
ICU allows collations to be customized beyond the basic language+country
|
|
set that is preloaded by <command>initdb</command>. Users are encouraged
|
|
to define their own collation objects that make use of these facilities to
|
|
suit the sorting behavior to their requirements.
|
|
See <ulink url="http://userguide.icu-project.org/locale"></ulink>
|
|
and <ulink url="http://userguide.icu-project.org/collation/api"></ulink> for
|
|
information on ICU locale naming. The set of acceptable names and
|
|
attributes depends on the particular ICU version.
|
|
</para>
|
|
|
|
<para>
|
|
Here are some examples:
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>CREATE COLLATION "de-u-co-phonebk-x-icu" (provider = icu, locale = 'de-u-co-phonebk');</literal></term>
|
|
<term><literal>CREATE COLLATION "de-u-co-phonebk-x-icu" (provider = icu, locale = 'de@collation=phonebook');</literal></term>
|
|
<listitem>
|
|
<para>German collation with phone book collation type</para>
|
|
<para>
|
|
The first example selects the ICU locale using a <quote>language
|
|
tag</quote> per BCP 47. The second example uses the traditional
|
|
ICU-specific locale syntax. The first style is preferred going
|
|
forward, but it is not supported by older ICU versions.
|
|
</para>
|
|
<para>
|
|
Note that you can name the collation objects in the SQL environment
|
|
anything you want. In this example, we follow the naming style that
|
|
the predefined collations use, which in turn also follow BCP 47, but
|
|
that is not required for user-defined collations.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>CREATE COLLATION "und-u-co-emoji-x-icu" (provider = icu, locale = 'und-u-co-emoji');</literal></term>
|
|
<term><literal>CREATE COLLATION "und-u-co-emoji-x-icu" (provider = icu, locale = '@collation=emoji');</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Root collation with Emoji collation type, per Unicode Technical Standard #51
|
|
</para>
|
|
<para>
|
|
Observe how in the traditional ICU locale naming system, the root
|
|
locale is selected by an empty string.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>CREATE COLLATION digitslast (provider = icu, locale = 'en-u-kr-latn-digit');</literal></term>
|
|
<term><literal>CREATE COLLATION digitslast (provider = icu, locale = 'en@colReorder=latn-digit');</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Sort digits after Latin letters. (The default is digits before letters.)
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>CREATE COLLATION upperfirst (provider = icu, locale = 'en-u-kf-upper');</literal></term>
|
|
<term><literal>CREATE COLLATION upperfirst (provider = icu, locale = 'en@colCaseFirst=upper');</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Sort upper-case letters before lower-case letters. (The default is
|
|
lower-case letters first.)
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>CREATE COLLATION special (provider = icu, locale = 'en-u-kf-upper-kr-latn-digit');</literal></term>
|
|
<term><literal>CREATE COLLATION special (provider = icu, locale = 'en@colCaseFirst=upper;colReorder=latn-digit');</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Combines both of the above options.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>CREATE COLLATION numeric (provider = icu, locale = 'en-u-kn-true');</literal></term>
|
|
<term><literal>CREATE COLLATION numeric (provider = icu, locale = 'en@colNumeric=yes');</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Numeric ordering, sorts sequences of digits by their numeric value,
|
|
for example: <literal>A-21</literal> < <literal>A-123</literal>
|
|
(also known as natural sort).
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
See <ulink url="http://unicode.org/reports/tr35/tr35-collation.html">Unicode
|
|
Technical Standard #35</ulink>
|
|
and <ulink url="https://tools.ietf.org/html/bcp47">BCP 47</ulink> for
|
|
details. The list of possible collation types (<literal>co</literal>
|
|
subtag) can be found in
|
|
the <ulink url="http://www.unicode.org/repos/cldr/trunk/common/bcp47/collation.xml">CLDR
|
|
repository</ulink>.
|
|
The <ulink url="https://ssl.icu-project.org/icu-bin/locexp">ICU Locale
|
|
Explorer</ulink> can be used to check the details of a particular locale
|
|
definition. The examples using the <literal>k*</literal> subtags require
|
|
at least ICU version 54.
|
|
</para>
|
|
|
|
<para>
|
|
Note that while this system allows creating collations that <quote>ignore
|
|
case</quote> or <quote>ignore accents</quote> or similar (using
|
|
the <literal>ks</literal> key), PostgreSQL does not at the moment allow
|
|
such collations to act in a truly case- or accent-insensitive manner. Any
|
|
strings that compare equal according to the collation but are not
|
|
byte-wise equal will be sorted according to their byte values.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
By design, ICU will accept almost any string as a locale name and match
|
|
it to the closest locale it can provide, using the fallback procedure
|
|
described in its documentation. Thus, there will be no direct feedback
|
|
if a collation specification is composed using features that the given
|
|
ICU installation does not actually support. It is therefore recommended
|
|
to create application-level test cases to check that the collation
|
|
definitions satisfy one's requirements.
|
|
</para>
|
|
</note>
|
|
</sect4>
|
|
|
|
<sect4 id="collation-copy">
|
|
<title>Copying Collations</title>
|
|
|
|
<para>
|
|
The command <xref linkend="sql-createcollation"/> can also be used to
|
|
create a new collation from an existing collation, which can be useful to
|
|
be able to use operating-system-independent collation names in
|
|
applications, create compatibility names, or use an ICU-provided collation
|
|
under a more readable name. For example:
|
|
<programlisting>
|
|
CREATE COLLATION german FROM "de_DE";
|
|
CREATE COLLATION french FROM "fr-x-icu";
|
|
</programlisting>
|
|
</para>
|
|
</sect4>
|
|
</sect3>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="multibyte">
|
|
<title>Character Set Support</title>
|
|
|
|
<indexterm zone="multibyte"><primary>character set</primary></indexterm>
|
|
|
|
<para>
|
|
The character set support in <productname>PostgreSQL</productname>
|
|
allows you to store text in a variety of character sets (also called
|
|
encodings), including
|
|
single-byte character sets such as the ISO 8859 series and
|
|
multiple-byte character sets such as <acronym>EUC</acronym> (Extended Unix
|
|
Code), UTF-8, and Mule internal code. All supported character sets
|
|
can be used transparently by clients, but a few are not supported
|
|
for use within the server (that is, as a server-side encoding).
|
|
The default character set is selected while
|
|
initializing your <productname>PostgreSQL</productname> database
|
|
cluster using <command>initdb</command>. It can be overridden when you
|
|
create a database, so you can have multiple
|
|
databases each with a different character set.
|
|
</para>
|
|
|
|
<para>
|
|
An important restriction, however, is that each database's character set
|
|
must be compatible with the database's <envar>LC_CTYPE</envar> (character
|
|
classification) and <envar>LC_COLLATE</envar> (string sort order) locale
|
|
settings. For <literal>C</literal> or
|
|
<literal>POSIX</literal> locale, any character set is allowed, but for other
|
|
libc-provided locales there is only one character set that will work
|
|
correctly.
|
|
(On Windows, however, UTF-8 encoding can be used with any locale.)
|
|
If you have ICU support configured, ICU-provided locales can be used
|
|
with most but not all server-side encodings.
|
|
</para>
|
|
|
|
<sect2 id="multibyte-charset-supported">
|
|
<title>Supported Character Sets</title>
|
|
|
|
<para>
|
|
<xref linkend="charset-table"/> shows the character sets available
|
|
for use in <productname>PostgreSQL</productname>.
|
|
</para>
|
|
|
|
<table id="charset-table">
|
|
<title><productname>PostgreSQL</productname> Character Sets</title>
|
|
<tgroup cols="7">
|
|
<thead>
|
|
<row>
|
|
<entry>Name</entry>
|
|
<entry>Description</entry>
|
|
<entry>Language</entry>
|
|
<entry>Server?</entry>
|
|
<entry>ICU?</entry>
|
|
<!--
|
|
The Bytes/Char field is populated by looking at the values returned
|
|
by pg_wchar_table.mblen function for each encoding.
|
|
-->
|
|
<entry>Bytes/Char</entry>
|
|
<entry>Aliases</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry><literal>BIG5</literal></entry>
|
|
<entry>Big Five</entry>
|
|
<entry>Traditional Chinese</entry>
|
|
<entry>No</entry>
|
|
<entry>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry><literal>WIN950</literal>, <literal>Windows950</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_CN</literal></entry>
|
|
<entry>Extended UNIX Code-CN</entry>
|
|
<entry>Simplified Chinese</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-3</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_JP</literal></entry>
|
|
<entry>Extended UNIX Code-JP</entry>
|
|
<entry>Japanese</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-3</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_JIS_2004</literal></entry>
|
|
<entry>Extended UNIX Code-JP, JIS X 0213</entry>
|
|
<entry>Japanese</entry>
|
|
<entry>Yes</entry>
|
|
<entry>No</entry>
|
|
<entry>1-3</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_KR</literal></entry>
|
|
<entry>Extended UNIX Code-KR</entry>
|
|
<entry>Korean</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-3</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>EUC_TW</literal></entry>
|
|
<entry>Extended UNIX Code-TW</entry>
|
|
<entry>Traditional Chinese, Taiwanese</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-3</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>GB18030</literal></entry>
|
|
<entry>National Standard</entry>
|
|
<entry>Chinese</entry>
|
|
<entry>No</entry>
|
|
<entry>No</entry>
|
|
<entry>1-4</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>GBK</literal></entry>
|
|
<entry>Extended National Standard</entry>
|
|
<entry>Simplified Chinese</entry>
|
|
<entry>No</entry>
|
|
<entry>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry><literal>WIN936</literal>, <literal>Windows936</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_5</literal></entry>
|
|
<entry>ISO 8859-5, <acronym>ECMA</acronym> 113</entry>
|
|
<entry>Latin/Cyrillic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_6</literal></entry>
|
|
<entry>ISO 8859-6, <acronym>ECMA</acronym> 114</entry>
|
|
<entry>Latin/Arabic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_7</literal></entry>
|
|
<entry>ISO 8859-7, <acronym>ECMA</acronym> 118</entry>
|
|
<entry>Latin/Greek</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISO_8859_8</literal></entry>
|
|
<entry>ISO 8859-8, <acronym>ECMA</acronym> 121</entry>
|
|
<entry>Latin/Hebrew</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>JOHAB</literal></entry>
|
|
<entry><acronym>JOHAB</acronym></entry>
|
|
<entry>Korean (Hangul)</entry>
|
|
<entry>No</entry>
|
|
<entry>No</entry>
|
|
<entry>1-3</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>KOI8R</literal></entry>
|
|
<entry><acronym>KOI</acronym>8-R</entry>
|
|
<entry>Cyrillic (Russian)</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>KOI8</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>KOI8U</literal></entry>
|
|
<entry><acronym>KOI</acronym>8-U</entry>
|
|
<entry>Cyrillic (Ukrainian)</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN1</literal></entry>
|
|
<entry>ISO 8859-1, <acronym>ECMA</acronym> 94</entry>
|
|
<entry>Western European</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO88591</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN2</literal></entry>
|
|
<entry>ISO 8859-2, <acronym>ECMA</acronym> 94</entry>
|
|
<entry>Central European</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO88592</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN3</literal></entry>
|
|
<entry>ISO 8859-3, <acronym>ECMA</acronym> 94</entry>
|
|
<entry>South European</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO88593</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN4</literal></entry>
|
|
<entry>ISO 8859-4, <acronym>ECMA</acronym> 94</entry>
|
|
<entry>North European</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO88594</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN5</literal></entry>
|
|
<entry>ISO 8859-9, <acronym>ECMA</acronym> 128</entry>
|
|
<entry>Turkish</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO88599</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN6</literal></entry>
|
|
<entry>ISO 8859-10, <acronym>ECMA</acronym> 144</entry>
|
|
<entry>Nordic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885910</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN7</literal></entry>
|
|
<entry>ISO 8859-13</entry>
|
|
<entry>Baltic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885913</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN8</literal></entry>
|
|
<entry>ISO 8859-14</entry>
|
|
<entry>Celtic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885914</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN9</literal></entry>
|
|
<entry>ISO 8859-15</entry>
|
|
<entry>LATIN1 with Euro and accents</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885915</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>LATIN10</literal></entry>
|
|
<entry>ISO 8859-16, <acronym>ASRO</acronym> SR 14111</entry>
|
|
<entry>Romanian</entry>
|
|
<entry>Yes</entry>
|
|
<entry>No</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ISO885916</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>MULE_INTERNAL</literal></entry>
|
|
<entry>Mule internal code</entry>
|
|
<entry>Multilingual Emacs</entry>
|
|
<entry>Yes</entry>
|
|
<entry>No</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>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry><literal>Mskanji</literal>, <literal>ShiftJIS</literal>, <literal>WIN932</literal>, <literal>Windows932</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>SHIFT_JIS_2004</literal></entry>
|
|
<entry>Shift JIS, JIS X 0213</entry>
|
|
<entry>Japanese</entry>
|
|
<entry>No</entry>
|
|
<entry>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>SQL_ASCII</literal></entry>
|
|
<entry>unspecified (see text)</entry>
|
|
<entry><emphasis>any</emphasis></entry>
|
|
<entry>Yes</entry>
|
|
<entry>No</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>No</entry>
|
|
<entry>1-2</entry>
|
|
<entry><literal>WIN949</literal>, <literal>Windows949</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>UTF8</literal></entry>
|
|
<entry>Unicode, 8-bit</entry>
|
|
<entry><emphasis>all</emphasis></entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1-4</entry>
|
|
<entry><literal>Unicode</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN866</literal></entry>
|
|
<entry>Windows CP866</entry>
|
|
<entry>Cyrillic</entry>
|
|
<entry>Yes</entry>
|
|
<entry>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ALT</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN874</literal></entry>
|
|
<entry>Windows CP874</entry>
|
|
<entry>Thai</entry>
|
|
<entry>Yes</entry>
|
|
<entry>No</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>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>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>WIN</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>WIN1252</literal></entry>
|
|
<entry>Windows CP1252</entry>
|
|
<entry>Western European</entry>
|
|
<entry>Yes</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>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>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>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>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>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>Yes</entry>
|
|
<entry>1</entry>
|
|
<entry><literal>ABC</literal>, <literal>TCVN</literal>, <literal>TCVN5712</literal>, <literal>VSCII</literal></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>
|
|
Not all client <acronym>API</acronym>s support all the listed character sets. For example, the
|
|
<productname>PostgreSQL</productname>
|
|
JDBC driver does not support <literal>MULE_INTERNAL</literal>, <literal>LATIN6</literal>,
|
|
<literal>LATIN8</literal>, and <literal>LATIN10</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
The <literal>SQL_ASCII</literal> setting behaves considerably differently
|
|
from the other settings. When the server character set is
|
|
<literal>SQL_ASCII</literal>, 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</literal>. 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</literal> 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</command> defines the default character set (encoding)
|
|
for a <productname>PostgreSQL</productname> cluster. For example,
|
|
|
|
<screen>
|
|
initdb -E EUC_JP
|
|
</screen>
|
|
|
|
sets the default character set to
|
|
<literal>EUC_JP</literal> (Extended Unix Code for Japanese). You
|
|
can use <option>--encoding</option> instead of
|
|
<option>-E</option> if you prefer longer option strings.
|
|
If no <option>-E</option> or <option>--encoding</option> option is
|
|
given, <command>initdb</command> attempts to determine the appropriate
|
|
encoding to use based on the specified or default locale.
|
|
</para>
|
|
|
|
<para>
|
|
You can specify a non-default encoding at database creation time,
|
|
provided that the encoding is compatible with the selected locale:
|
|
|
|
<screen>
|
|
createdb -E EUC_KR -T template0 --lc-collate=ko_KR.euckr --lc-ctype=ko_KR.euckr korean
|
|
</screen>
|
|
|
|
This will create a database named <literal>korean</literal> that
|
|
uses the character set <literal>EUC_KR</literal>, and locale <literal>ko_KR</literal>.
|
|
Another way to accomplish this is to use this SQL command:
|
|
|
|
<programlisting>
|
|
CREATE DATABASE korean WITH ENCODING 'EUC_KR' LC_COLLATE='ko_KR.euckr' LC_CTYPE='ko_KR.euckr' TEMPLATE=template0;
|
|
</programlisting>
|
|
|
|
Notice that the above commands specify copying the <literal>template0</literal>
|
|
database. When copying any other database, the encoding and locale
|
|
settings cannot be changed from those of the source database, because
|
|
that might result in corrupt data. For more information see
|
|
<xref linkend="manage-ag-templatedbs"/>.
|
|
</para>
|
|
|
|
<para>
|
|
The encoding for a database is stored in the system catalog
|
|
<literal>pg_database</literal>. You can see it by using the
|
|
<command>psql</command> <option>-l</option> option or the
|
|
<command>\l</command> command.
|
|
|
|
<screen>
|
|
$ <userinput>psql -l</userinput>
|
|
List of databases
|
|
Name | Owner | Encoding | Collation | Ctype | Access Privileges
|
|
-----------+----------+-----------+-------------+-------------+-------------------------------------
|
|
clocaledb | hlinnaka | SQL_ASCII | C | C |
|
|
englishdb | hlinnaka | UTF8 | en_GB.UTF8 | en_GB.UTF8 |
|
|
japanese | hlinnaka | UTF8 | ja_JP.UTF8 | ja_JP.UTF8 |
|
|
korean | hlinnaka | EUC_KR | ko_KR.euckr | ko_KR.euckr |
|
|
postgres | hlinnaka | UTF8 | fi_FI.UTF8 | fi_FI.UTF8 |
|
|
template0 | hlinnaka | UTF8 | fi_FI.UTF8 | fi_FI.UTF8 | {=c/hlinnaka,hlinnaka=CTc/hlinnaka}
|
|
template1 | hlinnaka | UTF8 | fi_FI.UTF8 | fi_FI.UTF8 | {=c/hlinnaka,hlinnaka=CTc/hlinnaka}
|
|
(7 rows)
|
|
</screen>
|
|
</para>
|
|
|
|
<important>
|
|
<para>
|
|
On most modern operating systems, <productname>PostgreSQL</productname>
|
|
can determine which character set is implied by the <envar>LC_CTYPE</envar>
|
|
setting, and it will enforce that only the matching database encoding is
|
|
used. On older systems it is your responsibility to ensure that you use
|
|
the encoding expected by the locale you have selected. A mistake in
|
|
this area is likely to lead to strange behavior of locale-dependent
|
|
operations such as sorting.
|
|
</para>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</productname> will allow superusers to create
|
|
databases with <literal>SQL_ASCII</literal> encoding even when
|
|
<envar>LC_CTYPE</envar> is not <literal>C</literal> or <literal>POSIX</literal>. As noted
|
|
above, <literal>SQL_ASCII</literal> does not enforce that the data stored in
|
|
the database has any particular encoding, and so this choice poses risks
|
|
of locale-dependent misbehavior. Using this combination of settings is
|
|
deprecated and may someday be forbidden altogether.
|
|
</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</literal> system catalog. <productname>PostgreSQL</productname>
|
|
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>KOI8R</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>KOI8R</literal></entry>
|
|
<entry><emphasis>KOI8R</emphasis>,
|
|
<literal>ISO_8859_5</literal>,
|
|
<literal>MULE_INTERNAL</literal>,
|
|
<literal>UTF8</literal>,
|
|
<literal>WIN866</literal>,
|
|
<literal>WIN1251</literal>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>KOI8U</literal></entry>
|
|
<entry><emphasis>KOI8U</emphasis>,
|
|
<literal>UTF8</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>KOI8R</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>KOI8R</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>KOI8R</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>
|
|
<application>libpq</application> (<xref linkend="libpq-control"/>) has functions to control the client encoding.
|
|
</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</replaceable>';
|
|
</programlisting>
|
|
|
|
Also you can use the standard SQL syntax <literal>SET NAMES</literal>
|
|
for this purpose:
|
|
|
|
<programlisting>
|
|
SET NAMES '<replaceable>value</replaceable>';
|
|
</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</varname> 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, and some
|
|
Japanese characters are returned that do not have a representation in
|
|
<literal>LATIN1</literal> — an error is reported.
|
|
</para>
|
|
|
|
<para>
|
|
If the client character set is defined as <literal>SQL_ASCII</literal>,
|
|
encoding conversion is disabled, regardless of the server's character
|
|
set. Just as for the server, use of <literal>SQL_ASCII</literal> 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><citetitle>CJKV Information Processing: Chinese, Japanese, Korean & Vietnamese Computing</citetitle></term>
|
|
|
|
<listitem>
|
|
<para>
|
|
Contains detailed explanations of <literal>EUC_JP</literal>,
|
|
<literal>EUC_CN</literal>, <literal>EUC_KR</literal>,
|
|
<literal>EUC_TW</literal>.
|
|
</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 3629</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
<acronym>UTF</acronym>-8 (8-bit UCS/Unicode Transformation
|
|
Format) is defined here.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
</chapter>
|