Localization</>
<para>
This chapter describes the available localization features from the
point of view of the administrator.
<productname>PostgreSQL</productname> supports localization with
two approaches:
<itemizedlist>
<listitem>
<para>
Using the locale features of the operating system to provide
locale-specific collation order, number formatting, translated
messages, and other aspects.
</para>
</listitem>
<listitem>
<para>
Providing a number of different character sets defined in the
<productname>PostgreSQL</productname> server, including
multiple-byte character sets, to support storing text in all
kinds of languages, and providing character set translation between
client and server.
</para>
</listitem>
</itemizedlist>
</para>
<sect1 id="locale">
<title>Locale Supportlocale
Locale support refers to an application respecting
cultural preferences regarding alphabets, sorting, number
formatting, etc. PostgreSQL uses the standard ISO
C and POSIX locale facilities provided by the server operating
system. For additional information refer to the documentation of your
system.
Overview</>
<para>
Locale support is automatically initialized when a database
cluster is created using <command>initdb</command>.
<command>initdb</command> will initialize the database cluster
with the locale setting of its execution environment 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 sets the locale to Swedish (<literal>sv</>) as spoken
in Sweden (<literal>SE</>). Other possibilities might be
<literal>en_US</> (U.S. English) and <literal>fr_CA</> (French
Canadian). If more than one character set can be useful for a
locale then the specifications look like this:
<literal>cs_CZ.ISO8859-2</>. What locales are available under what
names on your system depends on what was provided by the operating
system vendor and what was installed. (On most systems, the command
<literal>locale -a</> will provide a list of available locales.)
</para>
<para>
Occasionally it is useful to mix rules from several locales, e.g.,
use English collation rules but Spanish messages. To support that, a
set of locale subcategories exist that control only a certain
aspect of the localization rules:
<informaltable>
<tgroup cols="2">
<tbody>
<row>
<entry><envar>LC_COLLATE</></>
<entry>String sort order</>
</row>
<row>
<entry><envar>LC_CTYPE</></>
<entry>Character classification (What is a letter? 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 <literal>C</> or <literal>POSIX</>.
</para>
<para>
The nature of some locale categories is that their value has to be
fixed for the lifetime of a database cluster. That is, once
<command>initdb</command> has run, you cannot change them anymore.
<literal>LC_COLLATE</literal> and <literal>LC_CTYPE</literal> are
those categories. They affect the sort order of indexes, so they
must be kept fixed, or indexes on text columns will become corrupt.
<productname>PostgreSQL</productname> enforces this by recording
the values of <envar>LC_COLLATE</> and <envar>LC_CTYPE</> that are
seen by <command>initdb</>. The server automatically adopts
those two values when it is started.
</para>
<para>
The other locale categories can be changed as desired whenever the
server is running by setting the run-time configuration variables
that have the same name as the locale categories (see <xref
linkend="runtime-config-client-format"> for details). The defaults that are
chosen by <command>initdb</command> are actually only written into
the configuration file <filename>postgresql.conf</filename> to
serve as defaults when the server is started. If you delete 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 may
appear in different languages depending on where they originated.
</para>
<note>
<para>
When we speak of inheriting the locale from the execution
environment, this means the following on most operating systems:
For a given locale category, say the collation, the following
environment variables are consulted in this order until one is
found to be set: <envar>LC_ALL</envar>, <envar>LC_COLLATE</envar>
(the variable corresponding to the respective category),
<envar>LANG</envar>. If none of these environment variables are
set then the locale defaults to <literal>C</literal>.
</para>
<para>
Some message localization libraries also look at the environment
variable <envar>LANGUAGE</envar> which overrides all other locale
settings for the purpose of setting the language of messages. If
in doubt, please refer to the documentation of your operating
system, in particular the documentation about
<application>gettext</>, for more information.
</para>
</note>
<para>
To enable messages to be translated to the user's preferred language,
<acronym>NLS</acronym> must have been enabled at build time. This
choice is independent of the other locale support.
</para>
</sect2>
<sect2>
<title>Behavior</>
<para>
The locale settings influence the following SQL features:
<itemizedlist>
<listitem>
<para>
Sort order in queries using <literal>ORDER BY</> on textual data
<indexterm><primary>ORDER BY</><secondary>and locales</></indexterm>
</para>
</listitem>
<listitem>
<para>
The ability to use indexes with <literal>LIKE</> clauses
<indexterm><primary>LIKE</><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>
The <function>to_char</> family of functions
<indexterm><primary>to_char</><secondary>and locales</></indexterm>
</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.
</para>
</sect2>
<sect2>
<title>Problems</>
<para>
If locale support doesn't work in spite of the explanation above,
check that the locale support in your operating system is
correctly configured. To check what locales are installed on your
system, you may use the command <literal>locale -a</literal> if
your operating system provides it.
</para>
<para>
Check that <productname>PostgreSQL</> is actually using the locale
that you think it is. <envar>LC_COLLATE</> and <envar>LC_CTYPE</>
settings are determined at <command>initdb</> time and cannot be
changed without repeating <command>initdb</>. Other locale
settings including <envar>LC_MESSAGES</> and <envar>LC_MONETARY</>
are initially determined by the environment the server is started
in, 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="multibyte">
<title>Character Set Supportcharacter set
The character set support in PostgreSQL
allows you to store text in a variety of character sets, including
single-byte character sets such as the ISO 8859 series and
multiple-byte character sets such as EUC (Extended Unix
Code), UTF-8, and Mule internal code. All character sets can be
used transparently throughout the server. (If you use extension
functions from other sources, it depends on whether they wrote
their code correctly.) The default character set is selected while
initializing your PostgreSQL database
cluster using initdb. It can be overridden when you
create a database using createdb or by using the
SQL command CREATE DATABASE. So you can have multiple
databases each with a different character set.
Supported Character Sets shows the character sets available
for use in the server.
Not all APIs support all the listed character sets. For example, the
PostgreSQL
JDBC driver does not support MULE_INTERNAL, LATIN6,
LATIN8, and LATIN10.
The SQL_ASCII setting behaves considerably differently
from the other settings. When the server character set is
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 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
SQL_ASCII setting, because
PostgreSQL will be unable to help you by
converting or validating non-ASCII characters.
Setting the Character Setinitdb defines the default character set
for a PostgreSQL cluster. For example,
initdb -E EUC_JP
sets the default character set (encoding) to
EUC_JP (Extended Unix Code for Japanese). You
can use instead of
if you prefer to type longer option strings.
If no option is
given, initdb attempts to determine the appropriate
encoding to use based on the specified or default locale.
You can create a database with a different character set:
createdb -E EUC_KR korean
This will create a database named korean that
uses the character set EUC_KR. Another way to
accomplish this is to use this SQL command:
CREATE DATABASE korean WITH ENCODING 'EUC_KR';
The encoding for a database is stored in the system catalog
pg_database. You can see that by using the
option or the \l command
of psql.
$ psql -l
List of databases
Database | Owner | Encoding
---------------+---------+---------------
euc_cn | t-ishii | EUC_CN
euc_jp | t-ishii | EUC_JP
euc_kr | t-ishii | EUC_KR
euc_tw | t-ishii | EUC_TW
mule_internal | t-ishii | MULE_INTERNAL
postgres | t-ishii | EUC_JP
regression | t-ishii | SQL_ASCII
template1 | t-ishii | EUC_JP
test | t-ishii | EUC_JP
utf8 | t-ishii | UTF8
(9 rows)
Although you can specify any encoding you want for a database, it is
unwise to choose an encoding that is not what is expected by the locale
you have selected. The LC_COLLATE and
LC_CTYPE settings imply a particular encoding,
and locale-dependent operations (such as sorting) are likely to
misinterpret data that is in an incompatible encoding.
Since these locale settings are frozen by initdb, the
apparent flexibility to use different encodings in different databases
of a cluster is more theoretical than real. It is likely that these
mechanisms will be revisited in future versions of
PostgreSQL.
One way to use multiple encodings safely is to set the locale to
C or POSIX during initdb, thus
disabling any real locale awareness.
Automatic Character Set Conversion Between Server and ClientPostgreSQL supports automatic
character set conversion between server and client for certain
character sets. The conversion information is stored in the
pg_conversion system catalog. You can create a new
conversion by using the SQL command CREATE
CONVERSION. PostgreSQL comes with some
predefined conversions. They are listed in .
Client/Server Character Set ConversionsServer Character SetAvailable Client Character SetsBIG5not supported as a server encodingEUC_CNEUC_CN,
MULE_INTERNAL,
UTF8EUC_JPEUC_JP,
MULE_INTERNAL,
SJIS,
UTF8EUC_KREUC_KR,
MULE_INTERNAL,
UTF8EUC_TWEUC_TW,
BIG5,
MULE_INTERNAL,
UTF8GB18030not supported as a server encodingGBKnot supported as a server encodingISO_8859_5ISO_8859_5,
KOI8,
MULE_INTERNAL,
UTF8,
WIN866,
WIN1251ISO_8859_6ISO_8859_6,
UTF8ISO_8859_7ISO_8859_7,
UTF8ISO_8859_8ISO_8859_8,
UTF8JOHABJOHAB,
UTF8KOI8KOI8,
ISO_8859_5,
MULE_INTERNAL,
UTF8,
WIN866,
WIN1251LATIN1LATIN1,
MULE_INTERNAL,
UTF8LATIN2LATIN2,
MULE_INTERNAL,
UTF8,
WIN1250LATIN3LATIN3,
MULE_INTERNAL,
UTF8LATIN4LATIN4,
MULE_INTERNAL,
UTF8LATIN5LATIN5,
UTF8LATIN6LATIN6,
UTF8LATIN7LATIN7,
UTF8LATIN8LATIN8,
UTF8LATIN9LATIN9,
UTF8LATIN10LATIN10,
UTF8MULE_INTERNALMULE_INTERNAL,
BIG5,
EUC_CN,
EUC_JP,
EUC_KR,
EUC_TW,
ISO_8859_5,
KOI8,
LATIN1 to LATIN4,
SJIS,
WIN866,
WIN1250,
WIN1251SJISnot supported as a server encodingSQL_ASCIIany (no conversion will be performed)UHCnot supported as a server encodingUTF8all supported encodingsWIN866WIN866,
ISO_8859_5,
KOI8,
MULE_INTERNAL,
UTF8,
WIN1251WIN874WIN874,
UTF8WIN1250WIN1250,
LATIN2,
MULE_INTERNAL,
UTF8WIN1251WIN1251,
ISO_8859_5,
KOI8,
MULE_INTERNAL,
UTF8,
WIN866WIN1252WIN1252,
UTF8WIN1256WIN1256,
UTF8WIN1258WIN1258,
UTF8
To enable automatic character set conversion, you have to
tell PostgreSQL the character set
(encoding) you would like to use in the client. There are several
ways to accomplish this:
Using the \encoding command in
psql.
\encoding allows you to change client
encoding on the fly. For
example, to change the encoding to SJIS, type:
\encoding SJIS
Using libpq functions.
\encoding actually calls
PQsetClientEncoding() for its purpose.
int PQsetClientEncoding(PGconn *conn, const char *encoding);
where conn is a connection to the server,
and encoding is the encoding you
want to use. If the function successfully sets the encoding, it returns 0,
otherwise -1. The current encoding for this connection can be determined by
using:
int PQclientEncoding(const PGconn *conn);
Note that it returns the encoding ID, not a symbolic string
such as EUC_JP. To convert an encoding ID to an encoding name, you
can use:
char *pg_encoding_to_char(int encoding_id);
Using SET client_encoding TO.
Setting the client encoding can be done with this SQL command:
SET CLIENT_ENCODING TO 'value';
Also you can use the more standard SQL syntax SET NAMES for this purpose:
SET NAMES 'value';
To query the current client encoding:
SHOW client_encoding;
To return to the default encoding:
RESET client_encoding;
Using PGCLIENTENCODING. If the environment variable
PGCLIENTENCODING 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.)
Using the configuration variable . If the
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.)
If the conversion of a particular character is not possible
— suppose you chose EUC_JP for the
server and LATIN1 for the client, then some
Japanese characters cannot be converted to
LATIN1 — it is transformed to its
hexadecimal byte values in parentheses, e.g.,
(826C).
If the client character set is defined as SQL_ASCII,
encoding conversion is disabled, regardless of the server's character
set. Just as for the server, use of SQL_ASCII is unwise
unless you are working with all-ASCII data.
Further Reading
These are good sources to start learning about various kinds of encoding
systems.
An extensive collection of documents about character sets, encodings,
and code pages.
Detailed explanations of EUC_JP,
EUC_CN, EUC_KR,
EUC_TW appear in section 3.2.
The web site of the Unicode Consortium
RFC 2044
UTF-8 is defined here.