This chapter describes the available localization features from the point of view of the administrator. PostgreSQL supports two localization facilities: 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 and . 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 . locale 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. Locale support is automatically initialized when a database cluster is created using initdb. initdb 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 initdb exactly which locale to use by specifying the --locale option. For example: initdb --locale=sv_SE This example for Unix systems sets the locale to Swedish (sv) as spoken in Sweden (SE). Other possibilities might include en_US (U.S. English) and fr_CA (French Canadian). If more than one character set can be used for a locale then the specifications can take the form language_territory.codeset. For example, fr_BE.UTF-8 represents the French language (fr) as spoken in Belgium (BE), with a UTF-8 character set encoding. 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 locale -a will provide a list of available locales. Windows uses more verbose locale names, such as German_Germany or Swedish_Sweden.1252, but the principles are the same. 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: LC_COLLATE String sort order LC_CTYPE Character classification (What is a letter? Its upper-case equivalent?) LC_MESSAGES Language of messages LC_MONETARY Formatting of currency amounts LC_NUMERIC Formatting of numbers LC_TIME Formatting of dates and times The category names translate into names of initdb 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 initdb --locale=fr_CA --lc-monetary=en_US. If you want the system to behave as if it had no locale support, use the special locale name C, or equivalently POSIX. 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. LC_COLLATE and LC_CTYPE 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 .) The default values for these categories are determined when initdb is run, and those values are used when new databases are created, unless specified otherwise in the CREATE DATABASE command. 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 for details). The values that are chosen by initdb are actually only written into the configuration file postgresql.conf to serve as defaults when the server is started. If you remove these assignments from postgresql.conf then the server will inherit the settings from its execution environment. 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. 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: LC_ALL, LC_COLLATE (or the variable corresponding to the respective category), LANG. If none of these environment variables are set then the locale defaults to C. Some message localization libraries also look at the environment variable LANGUAGE 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 gettext. To enable messages to be translated to the user's preferred language, NLS must have been selected at build time (configure --enable-nls). All other locale support is built in automatically. The locale settings influence the following SQL features: Sort order in queries using ORDER BY or the standard comparison operators on textual data ORDER BYand locales The upper, lower, and initcap functions upperand locales lowerand locales Pattern matching operators (LIKE, SIMILAR TO, and POSIX-style regular expressions); locales affect both case insensitive matching and the classification of characters by character-class regular expressions LIKEand locales regular expressionsand locales The to_char family of functions to_charand locales The ability to use indexes with LIKE clauses The drawback of using locales other than C or POSIX in PostgreSQL is its performance impact. It slows character handling and prevents ordinary indexes from being used by LIKE. For this reason use locales only if you actually need them. As a workaround to allow PostgreSQL to use indexes with 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 for more information. Another approach is to create indexes using the C collation, as discussed in . 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 locale -a if your operating system provides it. Check that PostgreSQL is actually using the locale that you think it is. The LC_COLLATE and LC_CTYPE settings are determined when a database is created, and cannot be changed except by creating a new database. Other locale settings including LC_MESSAGES and 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 SHOW command. The directory src/test/locale in the source distribution contains a test suite for PostgreSQL's locale support. 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. Maintaining catalogs of message translations requires the on-going efforts of many volunteers that want to see 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 or write to the developers' mailing list. collation 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 LC_COLLATE and LC_CTYPE settings of a database cannot be changed after its creation. Conceptually, every expression of a collatable data type has a collation. (The built-in collatable data types are text, varchar, and char. 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. The collation of an expression can be the default 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. 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 ORDER BY clauses and function or operator calls such as <. The collation to apply for an ORDER BY 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 lower, upper, and initcap; by pattern matching operators; and by to_char and related functions. 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. The collation derivation 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 COLLATE 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: 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. 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. 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. For example, consider this table definition: CREATE TABLE test1 ( a text COLLATE "de_DE", b text COLLATE "es_ES", ... ); Then in SELECT a < 'foo' FROM test1; the < comparison is performed according to de_DE rules, because the expression combines an implicitly derived collation with the default collation. But in SELECT a < ('foo' COLLATE "fr_FR") FROM test1; the comparison is performed using fr_FR rules, because the explicit collation derivation overrides the implicit one. Furthermore, given SELECT a < b FROM test1; the parser cannot determine which collation to apply, since the a and b columns have conflicting implicit collations. Since the < 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: SELECT a < b COLLATE "de_DE" FROM test1; or equivalently SELECT a COLLATE "de_DE" < b FROM test1; On the other hand, the structurally similar case SELECT a || b FROM test1; does not result in an error, because the || operator does not care about collations: its result is the same regardless of the collation. 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 SELECT * FROM test1 ORDER BY a || 'foo'; the ordering will be done according to de_DE rules. But this query: SELECT * FROM test1 ORDER BY a || b; results in an error, because even though the || operator doesn't need to know a collation, the ORDER BY clause does. As before, the conflict can be resolved with an explicit collation specifier: SELECT * FROM test1 ORDER BY a || b COLLATE "fr_FR"; A collation is an SQL schema object that maps an SQL name to operating system locales. In particular, it maps to a combination of LC_COLLATE and LC_CTYPE. (As the name would suggest, the main purpose of a collation is to set LC_COLLATE, which controls the sort order. But it is rarely necessary in practice to have an LC_CTYPE setting that is different from LC_COLLATE, so it is more convenient to collect these under one concept than to create another infrastructure for setting LC_CTYPE per expression.) Also, a collation is tied to a character set encoding (see ). The same collation name may exist for different encodings. On all platforms, the collations named default, C, and POSIX are available. Additional collations may be available depending on operating system support. The default collation selects the LC_COLLATE and LC_CTYPE values specified at database creation time. The C and POSIX collations both specify traditional C behavior, in which only the ASCII letters A through Z are treated as letters, and sorting is done strictly by character code byte values. If the operating system provides support for using multiple locales within a single program (newlocale and related functions), then when a database cluster is initialized, initdb populates the system catalog pg_collation 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 de_DE.utf8. initdb would then create a collation named de_DE.utf8 for encoding UTF8 that has both LC_COLLATE and LC_CTYPE set to de_DE.utf8. It will also create a collation with the .utf8 tag stripped off the name. So you could also use the collation under the name de_DE, 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. In case a collation is needed that has different values for LC_COLLATE and LC_CTYPE, a new collation may be created using the 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. Within any particular database, only collations that use that database's encoding are of interest. Other entries in pg_collation are ignored. Thus, a stripped collation name such as de_DE 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 default, C, and POSIX collations can be used regardless of the database encoding. PostgreSQL considers distinct collation objects to be incompatible even when they have identical properties. Thus for example, SELECT a COLLATE "C" < b COLLATE "POSIX" FROM test1; will draw an error even though the C and POSIX collations have identical behaviors. Mixing stripped and non-stripped collation names is therefore not recommended. character set The character set support in PostgreSQL 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 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 PostgreSQL database cluster using initdb. It can be overridden when you create a database, so you can have multiple databases each with a different character set. An important restriction, however, is that each database's character set must be compatible with the database's LC_CTYPE (character classification) and LC_COLLATE (string sort order) locale settings. For C or 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.) shows the character sets available for use in PostgreSQL. Name Description Language Server? Bytes/Char Aliases BIG5 Big Five Traditional Chinese No 1-2 WIN950, Windows950 EUC_CN Extended UNIX Code-CN Simplified Chinese Yes 1-3 EUC_JP Extended UNIX Code-JP Japanese Yes 1-3 EUC_JIS_2004 Extended UNIX Code-JP, JIS X 0213 Japanese Yes 1-3 EUC_KR Extended UNIX Code-KR Korean Yes 1-3 EUC_TW Extended UNIX Code-TW Traditional Chinese, Taiwanese Yes 1-3 GB18030 National Standard Chinese No 1-4 GBK Extended National Standard Simplified Chinese No 1-2 WIN936, Windows936 ISO_8859_5 ISO 8859-5, ECMA 113 Latin/Cyrillic Yes 1 ISO_8859_6 ISO 8859-6, ECMA 114 Latin/Arabic Yes 1 ISO_8859_7 ISO 8859-7, ECMA 118 Latin/Greek Yes 1 ISO_8859_8 ISO 8859-8, ECMA 121 Latin/Hebrew Yes 1 JOHAB JOHAB Korean (Hangul) No 1-3 KOI8R KOI8-R Cyrillic (Russian) Yes 1 KOI8 KOI8U KOI8-U Cyrillic (Ukrainian) Yes 1 LATIN1 ISO 8859-1, ECMA 94 Western European Yes 1 ISO88591 LATIN2 ISO 8859-2, ECMA 94 Central European Yes 1 ISO88592 LATIN3 ISO 8859-3, ECMA 94 South European Yes 1 ISO88593 LATIN4 ISO 8859-4, ECMA 94 North European Yes 1 ISO88594 LATIN5 ISO 8859-9, ECMA 128 Turkish Yes 1 ISO88599 LATIN6 ISO 8859-10, ECMA 144 Nordic Yes 1 ISO885910 LATIN7 ISO 8859-13 Baltic Yes 1 ISO885913 LATIN8 ISO 8859-14 Celtic Yes 1 ISO885914 LATIN9 ISO 8859-15 LATIN1 with Euro and accents Yes 1 ISO885915 LATIN10 ISO 8859-16, ASRO SR 14111 Romanian Yes 1 ISO885916 MULE_INTERNAL Mule internal code Multilingual Emacs Yes 1-4 SJIS Shift JIS Japanese No 1-2 Mskanji, ShiftJIS, WIN932, Windows932 SHIFT_JIS_2004 Shift JIS, JIS X 0213 Japanese No 1-2 SQL_ASCII unspecified (see text) any Yes 1 UHC Unified Hangul Code Korean No 1-2 WIN949, Windows949 UTF8 Unicode, 8-bit all Yes 1-4 Unicode WIN866 Windows CP866 Cyrillic Yes 1 ALT WIN874 Windows CP874 Thai Yes 1 WIN1250 Windows CP1250 Central European Yes 1 WIN1251 Windows CP1251 Cyrillic Yes 1 WIN WIN1252 Windows CP1252 Western European Yes 1 WIN1253 Windows CP1253 Greek Yes 1 WIN1254 Windows CP1254 Turkish Yes 1 WIN1255 Windows CP1255 Hebrew Yes 1 WIN1256 Windows CP1256 Arabic Yes 1 WIN1257 Windows CP1257 Baltic Yes 1 WIN1258 Windows CP1258 Vietnamese Yes 1 ABC, TCVN, TCVN5712, VSCII Not all client 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. initdb defines the default character set (encoding) for a PostgreSQL cluster. For example, initdb -E EUC_JP sets the default character set to EUC_JP (Extended Unix Code for Japanese). You can use --encoding instead of -E if you prefer longer option strings. If no -E or --encoding option is given, initdb attempts to determine the appropriate encoding to use based on the specified or default locale. You can specify a non-default encoding at database creation time, provided that the encoding is compatible with the selected locale: createdb -E EUC_KR -T template0 --lc-collate=ko_KR.euckr --lc-ctype=ko_KR.euckr korean This will create a database named korean that uses the character set EUC_KR, and locale ko_KR. Another way to accomplish this is to use this SQL command: CREATE DATABASE korean WITH ENCODING 'EUC_KR' LC_COLLATE='ko_KR.euckr' LC_CTYPE='ko_KR.euckr' TEMPLATE=template0; Notice that the above commands specify copying the 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 . The encoding for a database is stored in the system catalog pg_database. You can see it by using the psql -l option or the \l command. $ psql -l 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) On most modern operating systems, PostgreSQL can determine which character set is implied by the 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. PostgreSQL will allow superusers to create databases with SQL_ASCII encoding even when LC_CTYPE is not C or POSIX. As noted above, 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. PostgreSQL supports automatic character set conversion between server and client for certain character set combinations. The conversion information is stored in the pg_conversion system catalog. PostgreSQL comes with some predefined conversions, as shown in . You can create a new conversion using the SQL command CREATE CONVERSION. Server Character Set Available Client Character Sets BIG5 not supported as a server encoding EUC_CN EUC_CN, MULE_INTERNAL, UTF8 EUC_JP EUC_JP, MULE_INTERNAL, SJIS, UTF8 EUC_KR EUC_KR, MULE_INTERNAL, UTF8 EUC_TW EUC_TW, BIG5, MULE_INTERNAL, UTF8 GB18030 not supported as a server encoding GBK not supported as a server encoding ISO_8859_5 ISO_8859_5, KOI8R, MULE_INTERNAL, UTF8, WIN866, WIN1251 ISO_8859_6 ISO_8859_6, UTF8 ISO_8859_7 ISO_8859_7, UTF8 ISO_8859_8 ISO_8859_8, UTF8 JOHAB JOHAB, UTF8 KOI8R KOI8R, ISO_8859_5, MULE_INTERNAL, UTF8, WIN866, WIN1251 KOI8U KOI8U, UTF8 LATIN1 LATIN1, MULE_INTERNAL, UTF8 LATIN2 LATIN2, MULE_INTERNAL, UTF8, WIN1250 LATIN3 LATIN3, MULE_INTERNAL, UTF8 LATIN4 LATIN4, MULE_INTERNAL, UTF8 LATIN5 LATIN5, UTF8 LATIN6 LATIN6, UTF8 LATIN7 LATIN7, UTF8 LATIN8 LATIN8, UTF8 LATIN9 LATIN9, UTF8 LATIN10 LATIN10, UTF8 MULE_INTERNAL MULE_INTERNAL, BIG5, EUC_CN, EUC_JP, EUC_KR, EUC_TW, ISO_8859_5, KOI8R, LATIN1 to LATIN4, SJIS, WIN866, WIN1250, WIN1251 SJIS not supported as a server encoding SQL_ASCII any (no conversion will be performed) UHC not supported as a server encoding UTF8 all supported encodings WIN866 WIN866, ISO_8859_5, KOI8R, MULE_INTERNAL, UTF8, WIN1251 WIN874 WIN874, UTF8 WIN1250 WIN1250, LATIN2, MULE_INTERNAL, UTF8 WIN1251 WIN1251, ISO_8859_5, KOI8R, MULE_INTERNAL, UTF8, WIN866 WIN1252 WIN1252, UTF8 WIN1253 WIN1253, UTF8 WIN1254 WIN1254, UTF8 WIN1255 WIN1255, UTF8 WIN1256 WIN1256, UTF8 WIN1257 WIN1257, UTF8 WIN1258 WIN1258, 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 libpq () has functions to control the client encoding. 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 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, and some Japanese characters are returned that do not have a representation in LATIN1 — an error is reported. 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. These are good sources to start learning about various kinds of encoding systems. CJKV Information Processing: Chinese, Japanese, Korean & Vietnamese Computing Contains detailed explanations of EUC_JP, EUC_CN, EUC_KR, EUC_TW. The web site of the Unicode Consortium. RFC 3629 UTF-8 (8-bit UCS/Unicode Transformation Format) is defined here.