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<!-- doc/src/sgml/charset.sgml -->
<chapter id="charset">
<title>Localization</title>
<para>
This chapter describes the available localization features from the
point of view of the administrator.
<productname>PostgreSQL</productname> supports two localization
facilities:
<itemizedlist>
<listitem>
<para>
Using the locale features of the operating system to provide
locale-specific collation order, number formatting, translated
messages, and other aspects.
This is covered in <xref linkend="locale"> and
<xref linkend="collation">.
</para>
</listitem>
<listitem>
<para>
Providing a number of different character sets to support storing text
in all kinds of languages, and providing character set translation
between client and server.
This is covered in <xref linkend="multibyte">.
</para>
</listitem>
</itemizedlist>
</para>
<sect1 id="locale">
<title>Locale Support</title>
<indexterm zone="locale"><primary>locale</></>
<para>
<firstterm>Locale</> support refers to an application respecting
cultural preferences regarding alphabets, sorting, number
formatting, etc. <productname>PostgreSQL</> uses the standard ISO
C and <acronym>POSIX</acronym> locale facilities provided by the server operating
system. For additional information refer to the documentation of your
system.
</para>
<sect2>
<title>Overview</title>
<para>
Locale support is automatically initialized when a database
cluster is created using <command>initdb</command>.
<command>initdb</command> will initialize the database cluster
with the locale setting of its execution environment by default,
so if your system is already set to use the locale that you want
in your database cluster then there is nothing else you need to
do. If you want to use a different locale (or you are not sure
which locale your system is set to), you can instruct
<command>initdb</command> exactly which locale to use by
specifying the <option>--locale</option> option. For example:
<screen>
initdb --locale=sv_SE
</screen>
</para>
<para>
This example for Unix systems sets the locale to Swedish
(<literal>sv</>) as spoken
in Sweden (<literal>SE</>). Other possibilities might include
<literal>en_US</> (U.S. English) and <literal>fr_CA</> (French
Canadian). If more than one character set can be used for a
locale then the specifications can take the form
<replaceable>language_territory.codeset</>. For example,
<literal>fr_BE.UTF-8</> represents the French language (fr) as
spoken in Belgium (BE), with a <acronym>UTF-8</> character set
encoding.
</para>
<para>
What locales are available on your
system under what names depends on what was provided by the operating
system vendor and what was installed. On most Unix systems, the command
<literal>locale -a</> will provide a list of available locales.
Windows uses more verbose locale names, such as <literal>German_Germany</>
or <literal>Swedish_Sweden.1252</>, but the principles are the same.
</para>
<para>
Occasionally it is useful to mix rules from several locales, e.g.,
use English collation rules but Spanish messages. To support that, a
set of locale subcategories exist that control only certain
aspects of the localization rules:
<informaltable>
<tgroup cols="2">
<tbody>
<row>
<entry><envar>LC_COLLATE</></>
<entry>String sort order</>
</row>
<row>
<entry><envar>LC_CTYPE</></>
<entry>Character classification (What is a letter? Its upper-case equivalent?)</>
</row>
<row>
<entry><envar>LC_MESSAGES</></>
<entry>Language of messages</>
</row>
<row>
<entry><envar>LC_MONETARY</></>
<entry>Formatting of currency amounts</>
</row>
<row>
<entry><envar>LC_NUMERIC</></>
<entry>Formatting of numbers</>
</row>
<row>
<entry><envar>LC_TIME</></>
<entry>Formatting of dates and times</>
</row>
</tbody>
</tgroup>
</informaltable>
The category names translate into names of
<command>initdb</command> options to override the locale choice
for a specific category. For instance, to set the locale to
French Canadian, but use U.S. rules for formatting currency, use
<literal>initdb --locale=fr_CA --lc-monetary=en_US</literal>.
</para>
<para>
If you want the system to behave as if it had no locale support,
use the special locale name <literal>C</>, or equivalently
<literal>POSIX</>.
</para>
<para>
Some locale categories must have their values
fixed when the database is created. You can use different settings
for different databases, but once a database is created, you cannot
change them for that database anymore. <literal>LC_COLLATE</literal>
and <literal>LC_CTYPE</literal> are these categories. They affect
the sort order of indexes, so they must be kept fixed, or indexes on
text columns would become corrupt.
(But you can alleviate this restriction using collations, as discussed
in <xref linkend="collation">.)
The default values for these
categories are determined when <command>initdb</command> is run, and
those values are used when new databases are created, unless
specified otherwise in the <command>CREATE DATABASE</command> command.
</para>
<para>
The other locale categories can be changed whenever desired
by setting the server configuration parameters
that have the same name as the locale categories (see <xref
linkend="runtime-config-client-format"> for details). The values
that are chosen by <command>initdb</command> are actually only written
into the configuration file <filename>postgresql.conf</filename> to
serve as defaults when the server is started. If you remove these
assignments from <filename>postgresql.conf</filename> then the
server will inherit the settings from its execution environment.
</para>
<para>
Note that the locale behavior of the server is determined by the
environment variables seen by the server, not by the environment
of any client. Therefore, be careful to configure the correct locale settings
before starting the server. A consequence of this is that if
client and server are set up in different locales, messages might
appear in different languages depending on where they originated.
</para>
<note>
<para>
When we speak of inheriting the locale from the execution
environment, this means the following on most operating systems:
For a given locale category, say the collation, the following
environment variables are consulted in this order until one is
found to be set: <envar>LC_ALL</envar>, <envar>LC_COLLATE</envar>
(or the variable corresponding to the respective category),
<envar>LANG</envar>. If none of these environment variables are
set then the locale defaults to <literal>C</literal>.
</para>
<para>
Some message localization libraries also look at the environment
variable <envar>LANGUAGE</envar> which overrides all other locale
settings for the purpose of setting the language of messages. If
in doubt, please refer to the documentation of your operating
system, in particular the documentation about
<application>gettext</>.
</para>
</note>
<para>
To enable messages to be translated to the user's preferred language,
<acronym>NLS</acronym> must have been selected at build time
(<literal>configure --enable-nls</>). All other locale support is
built in automatically.
</para>
</sect2>
<sect2>
<title>Behavior</title>
<para>
The locale settings influence the following SQL features:
<itemizedlist>
<listitem>
<para>
Sort order in queries using <literal>ORDER BY</> or the standard
comparison operators on textual data
<indexterm><primary>ORDER BY</><secondary>and locales</></indexterm>
</para>
</listitem>
<listitem>
<para>
The <function>upper</>, <function>lower</>, and <function>initcap</>
functions
<indexterm><primary>upper</><secondary>and locales</></indexterm>
<indexterm><primary>lower</><secondary>and locales</></indexterm>
</para>
</listitem>
<listitem>
<para>
Pattern matching operators (<literal>LIKE</>, <literal>SIMILAR TO</>,
and POSIX-style regular expressions); locales affect both case
insensitive matching and the classification of characters by
character-class regular expressions
<indexterm><primary>LIKE</><secondary>and locales</></indexterm>
<indexterm><primary>regular expressions</><secondary>and locales</></indexterm>
</para>
</listitem>
<listitem>
<para>
The <function>to_char</> family of functions
<indexterm><primary>to_char</><secondary>and locales</></indexterm>
</para>
</listitem>
<listitem>
<para>
The ability to use indexes with <literal>LIKE</> clauses
</para>
</listitem>
</itemizedlist>
</para>
<para>
The drawback of using locales other than <literal>C</> or
<literal>POSIX</> in <productname>PostgreSQL</> is its performance
impact. It slows character handling and prevents ordinary indexes
from being used by <literal>LIKE</>. For this reason use locales
only if you actually need them.
</para>
<para>
As a workaround to allow <productname>PostgreSQL</> to use indexes
with <literal>LIKE</> clauses under a non-C locale, several custom
operator classes exist. These allow the creation of an index that
performs a strict character-by-character comparison, ignoring
locale comparison rules. Refer to <xref linkend="indexes-opclass">
for more information. Another approach is to create indexes using
the <literal>C</> collation, as discussed in
<xref linkend="collation">.
</para>
</sect2>
<sect2>
<title>Problems</title>
<para>
If locale support doesn't work according to the explanation above,
check that the locale support in your operating system is
correctly configured. To check what locales are installed on your
system, you can use the command <literal>locale -a</literal> if
your operating system provides it.
</para>
<para>
Check that <productname>PostgreSQL</> is actually using the locale
that you think it is. The <envar>LC_COLLATE</> and <envar>LC_CTYPE</>
settings are determined when a database is created, and cannot be
changed except by creating a new database. Other locale
settings including <envar>LC_MESSAGES</> and <envar>LC_MONETARY</>
are initially determined by the environment the server is started
in, but can be changed on-the-fly. You can check the active locale
settings using the <command>SHOW</> command.
</para>
<para>
The directory <filename>src/test/locale</> in the source
distribution contains a test suite for
<productname>PostgreSQL</>'s locale support.
</para>
<para>
Client applications that handle server-side errors by parsing the
text of the error message will obviously have problems when the
server's messages are in a different language. Authors of such
applications are advised to make use of the error code scheme
instead.
</para>
<para>
Maintaining catalogs of message translations requires the on-going
efforts of many volunteers that want to see
<productname>PostgreSQL</> speak their preferred language well.
If messages in your language are currently not available or not fully
translated, your assistance would be appreciated. If you want to
help, refer to <xref linkend="nls"> or write to the developers'
mailing list.
</para>
</sect2>
</sect1>
<sect1 id="collation">
<title>Collation Support</title>
<indexterm zone="collation"><primary>collation</></>
<para>
The collation feature allows specifying the sort order and character
classification behavior of data per-column, or even per-operation.
This alleviates the restriction that the
<symbol>LC_COLLATE</symbol> and <symbol>LC_CTYPE</symbol> settings
of a database cannot be changed after its creation.
</para>
<sect2>
<title>Concepts</title>
<para>
Conceptually, every expression of a collatable data type has a
collation. (The built-in collatable data types are
<type>text</type>, <type>varchar</type>, and <type>char</type>.
User-defined base types can also be marked collatable, and of course
a domain over a collatable data type is collatable.) If the
expression is a column reference, the collation of the expression is the
defined collation of the column. If the expression is a constant, the
collation is the default collation of the data type of the
constant. The collation of a more complex expression is derived
from the collations of its inputs, as described below.
</para>
<para>
The collation of an expression can be the <quote>default</quote>
collation, which means the locale settings defined for the
database. It is also possible for an expression's collation to be
indeterminate. In such cases, ordering operations and other
operations that need to know the collation will fail.
</para>
<para>
When the database system has to perform an ordering or a character
classification, it uses the collation of the input expression. This
happens, for example, with <literal>ORDER BY</literal> clauses
and function or operator calls such as <literal><</literal>.
The collation to apply for an <literal>ORDER BY</literal> clause
is simply the collation of the sort key. The collation to apply for a
function or operator call is derived from the arguments, as described
below. In addition to comparison operators, collations are taken into
account by functions that convert between lower and upper case
letters, such as <function>lower</>, <function>upper</>, and
<function>initcap</>; by pattern matching operators; and by
<function>to_char</> and related functions.
</para>
<para>
For a function or operator call, the collation that is derived by
examining the argument collations is used at run time for performing
the specified operation. If the result of the function or operator
call is of a collatable data type, the collation is also used at parse
time as the defined collation of the function or operator expression,
in case there is a surrounding expression that requires knowledge of
its collation.
</para>
<para>
The <firstterm>collation derivation</firstterm> of an expression can be
implicit or explicit. This distinction affects how collations are
combined when multiple different collations appear in an
expression. An explicit collation derivation occurs when a
<literal>COLLATE</literal> clause is used; all other collation
derivations are implicit. When multiple collations need to be
combined, for example in a function call, the following rules are
used:
<orderedlist>
<listitem>
<para>
If any input expression has an explicit collation derivation, then
all explicitly derived collations among the input expressions must be
the same, otherwise an error is raised. If any explicitly
derived collation is present, that is the result of the
collation combination.
</para>
</listitem>
<listitem>
<para>
Otherwise, all input expressions must have the same implicit
collation derivation or the default collation. If any non-default
collation is present, that is the result of the collation combination.
Otherwise, the result is the default collation.
</para>
</listitem>
<listitem>
<para>
If there are conflicting non-default implicit collations among the
input expressions, then the combination is deemed to have indeterminate
collation. This is not an error condition unless the particular
function being invoked requires knowledge of the collation it should
apply. If it does, an error will be raised at run-time.
</para>
</listitem>
</orderedlist>
For example, consider this table definition:
<programlisting>
CREATE TABLE test1 (
a text COLLATE "de_DE",
b text COLLATE "es_ES",
...
);
</programlisting>
Then in
<programlisting>
SELECT a < 'foo' FROM test1;
</programlisting>
the <literal><</literal> comparison is performed according to
<literal>de_DE</literal> rules, because the expression combines an
implicitly derived collation with the default collation. But in
<programlisting>
SELECT a < ('foo' COLLATE "fr_FR") FROM test1;
</programlisting>
the comparison is performed using <literal>fr_FR</literal> rules,
because the explicit collation derivation overrides the implicit one.
Furthermore, given
<programlisting>
SELECT a < b FROM test1;
</programlisting>
the parser cannot determine which collation to apply, since the
<structfield>a</> and <structfield>b</> columns have conflicting
implicit collations. Since the <literal><</literal> operator
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;
</programlisting>
or equivalently
<programlisting>
SELECT a COLLATE "de_DE" < b FROM test1;
</programlisting>
On the other hand, the structurally similar case
<programlisting>
SELECT a || b FROM test1;
</programlisting>
does not result in an error, because the <literal>||</> operator
does not care about collations: its result is the same regardless
of the collation.
</para>
<para>
The collation assigned to a function or operator's combined input
expressions is also considered to apply to the function or operator's
result, if the function or operator delivers a result of a collatable
data type. So, in
<programlisting>
SELECT * FROM test1 ORDER BY a || 'foo';
</programlisting>
the ordering will be done according to <literal>de_DE</literal> rules.
But this query:
<programlisting>
SELECT * FROM test1 ORDER BY a || b;
</programlisting>
results in an error, because even though the <literal>||</> operator
doesn't need to know a collation, the <literal>ORDER BY</> 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>
<title>Managing Collations</title>
<para>
A collation is an SQL schema object that maps an SQL name to
operating system locales. In particular, it maps to a combination
of <symbol>LC_COLLATE</symbol> and <symbol>LC_CTYPE</symbol>. (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 collation
is tied to a character set encoding (see <xref linkend="multibyte">).
The same collation name may exist for different encodings.
</para>
<para>
On all platforms, the collations named <literal>default</>,
<literal>C</>, and <literal>POSIX</> are available. Additional
collations may be available depending on operating system support.
The <literal>default</> collation selects the <symbol>LC_COLLATE</symbol>
and <symbol>LC_CTYPE</symbol> values specified at database creation time.
The <literal>C</> and <literal>POSIX</> collations both specify
<quote>traditional C</> behavior, in which only the ASCII letters
<quote><literal>A</></quote> through <quote><literal>Z</></quote>
are treated as letters, and sorting is done strictly by character
code byte values.
</para>
<para>
If the operating system provides support for using multiple locales
within a single program (<function>newlocale</> and related functions),
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 on the operating
system at the time. 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>
In case a collation is needed that has different values for
<symbol>LC_COLLATE</symbol> and <symbol>LC_CTYPE</symbol>, a new
collation may be created using
the <xref linkend="sql-createcollation"> command. That command
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.
</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>C</>, and <literal>POSIX</> 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</> and <literal>POSIX</>
collations have identical behaviors. Mixing stripped and non-stripped
collation names is therefore not recommended.
</para>
</sect2>
</sect1>
<sect1 id="multibyte">
<title>Character Set Support</title>
<indexterm zone="multibyte"><primary>character set</></>
<para>
The character set support in <productname>PostgreSQL</productname>
allows you to store text in a variety of character sets (also called
encodings), including
single-byte character sets such as the ISO 8859 series and
multiple-byte character sets such as <acronym>EUC</> (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</>. 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</> (character
classification) and <envar>LC_COLLATE</> (string sort order) locale
settings. For <literal>C</> or
<literal>POSIX</> locale, any character set is allowed, but for other
locales there is only one character set that will work correctly.
(On Windows, however, UTF-8 encoding can be used with any locale.)
</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="6">
<thead>
<row>
<entry>Name</entry>
<entry>Description</entry>
<entry>Language</entry>
<entry>Server?</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>1-2</entry>
<entry><literal>WIN950</>, <literal>Windows950</></entry>
</row>
<row>
<entry><literal>EUC_CN</literal></entry>
<entry>Extended UNIX Code-CN</entry>
<entry>Simplified Chinese</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>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>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>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>1-3</entry>
<entry></entry>
</row>
<row>
<entry><literal>GB18030</literal></entry>
<entry>National Standard</entry>
<entry>Chinese</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>1-2</entry>
<entry><literal>WIN936</>, <literal>Windows936</></entry>
</row>
<row>
<entry><literal>ISO_8859_5</literal></entry>
<entry>ISO 8859-5, <acronym>ECMA</> 113</entry>
<entry>Latin/Cyrillic</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry></entry>
</row>
<row>
<entry><literal>ISO_8859_6</literal></entry>
<entry>ISO 8859-6, <acronym>ECMA</> 114</entry>
<entry>Latin/Arabic</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry></entry>
</row>
<row>
<entry><literal>ISO_8859_7</literal></entry>
<entry>ISO 8859-7, <acronym>ECMA</> 118</entry>
<entry>Latin/Greek</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry></entry>
</row>
<row>
<entry><literal>ISO_8859_8</literal></entry>
<entry>ISO 8859-8, <acronym>ECMA</> 121</entry>
<entry>Latin/Hebrew</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry></entry>
</row>
<row>
<entry><literal>JOHAB</literal></entry>
<entry><acronym>JOHAB</></entry>
<entry>Korean (Hangul)</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>1</entry>
<entry><literal>KOI8</></entry>
</row>
<row>
<entry><literal>KOI8U</literal></entry>
<entry><acronym>KOI</acronym>8-U</entry>
<entry>Cyrillic (Ukrainian)</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry></entry>
</row>
<row>
<entry><literal>LATIN1</literal></entry>
<entry>ISO 8859-1, <acronym>ECMA</> 94</entry>
<entry>Western European</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry><literal>ISO88591</></entry>
</row>
<row>
<entry><literal>LATIN2</literal></entry>
<entry>ISO 8859-2, <acronym>ECMA</> 94</entry>
<entry>Central European</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry><literal>ISO88592</></entry>
</row>
<row>
<entry><literal>LATIN3</literal></entry>
<entry>ISO 8859-3, <acronym>ECMA</> 94</entry>
<entry>South European</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry><literal>ISO88593</></entry>
</row>
<row>
<entry><literal>LATIN4</literal></entry>
<entry>ISO 8859-4, <acronym>ECMA</> 94</entry>
<entry>North European</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry><literal>ISO88594</></entry>
</row>
<row>
<entry><literal>LATIN5</literal></entry>
<entry>ISO 8859-9, <acronym>ECMA</> 128</entry>
<entry>Turkish</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry><literal>ISO88599</></entry>
</row>
<row>
<entry><literal>LATIN6</literal></entry>
<entry>ISO 8859-10, <acronym>ECMA</> 144</entry>
<entry>Nordic</entry>
<entry>Yes</entry>
<entry>1</entry>
<entry><literal>ISO885910</></entry>
</row>
<row>
<entry><literal>LATIN7</literal></entry>
<entry>ISO 8859-13</entry>
<entry>Baltic</entry>
<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><literal>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>SHIFT_JIS_2004</literal></entry>
<entry>Shift JIS, JIS X 0213</entry>
<entry>Japanese</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</></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 client <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 (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</> 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 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</>
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</>
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</> encoding even when
<envar>LC_CTYPE</> is not <literal>C</> or <literal>POSIX</>. As noted
above, <literal>SQL_ASCII</> 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</> 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>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</> (<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</>';
</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, 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</>,
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><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>