PostgreSQL 8.2.10 Documentation
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# 21.1. Locale Support

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.

## 21.1.1. Overview

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 sets the locale to Swedish (`sv`) as spoken in Sweden (`SE`). Other possibilities might be `en_US` (U.S. English) and `fr_CA` (French Canadian). If more than one character set can be useful for a locale then the specifications look like this: `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 `locale -a` will provide a list of available locales.)

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:

`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 `C` or `POSIX`.

The nature of some locale categories is that their value has to be fixed for the lifetime of a database cluster. That is, once `initdb` has run, you cannot change them anymore. `LC_COLLATE` and `LC_CTYPE` are those categories. They affect the sort order of indexes, so they must be kept fixed, or indexes on text columns will become corrupt. PostgreSQL enforces this by recording the values of `LC_COLLATE` and `LC_CTYPE` that are seen by `initdb`. The server automatically adopts those two values when it is started.

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 Section 17.10.2 for details). The defaults 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 delete 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 may appear in different languages depending on where they originated.

> Note: 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` (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, for more information.

To enable messages to be translated to the user's preferred language, NLS must have been enabled at build time. This choice is independent of the other locale support.

## 21.1.2. Behavior

The locale settings influence the following SQL features:

- Sort order in queries using `ORDER BY` on textual data

- The ability to use indexes with `LIKE` clauses

- The `upper`, `lower`, and `initcap` functions

- The `to_char` family of functions

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 Section 11.8 for more information.

## 21.1.3. Problems

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 `locale -a` if your operating system provides it.

Check that PostgreSQL is actually using the locale that you think it is. `LC_COLLATE` and `LC_CTYPE` settings are determined at `initdb` time and cannot be changed without repeating `initdb`. 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 Chapter 46 or write to the developers' mailing list.

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