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The character set support in PostgreSQL allows you to store text in avariety of character sets (also called encodings), includingsingle-byte character sets such as the ISO 8859 series andmultiple-byte character sets such as EUC (Extended Unix Code), UTF-8, and Muleinternal code. All supported character sets can be usedtransparently by clients, but a few are not supported for usewithin the server (that is, as a server-side encoding). The defaultcharacter set is selected while initializing your PostgreSQL database cluster using initdb. It can be overridden when you create adatabase, so you can have multiple databases each with a differentcharacter set.

An important restriction, however, is that each database'scharacter set must be compatible with the database's LC_CTYPE (character classification) and LC_COLLATE (string sort order) locale settings. ForC or POSIXlocale, any character set is allowed, but for other locales thereis only one character set that will work correctly. (On Windows,however, UTF-8 encoding can be used with any locale.)

22.3.1. Supported CharacterSets

Table 22-1 shows thecharacter sets available for use in PostgreSQL.

Table 22-1. PostgreSQLCharacter Sets

Not all client APIs supportall the listed character sets. For example, the PostgreSQL JDBC driver does not supportMULE_INTERNAL, LATIN6, LATIN8, andLATIN10.

The SQL_ASCII setting behavesconsiderably differently from the other settings. When the servercharacter set is SQL_ASCII, the serverinterprets byte values 0-127 according to the ASCII standard, whilebyte values 128-255 are taken as uninterpreted characters. Noencoding conversion will be done when the setting is SQL_ASCII. Thus, this setting is not so much adeclaration that a specific encoding is in use, as a declaration ofignorance about the encoding. In most cases, if you are workingwith any non-ASCII data, it is unwise to use the SQL_ASCII setting because PostgreSQL will be unable to help you byconverting or validating non-ASCII characters.

22.3.2. Settingthe Character Set

initdb defines the default characterset (encoding) for a PostgreSQLcluster. For example,

sets the default character set to EUC_JP (Extended Unix Code for Japanese). You canuse --encoding instead of -E if you prefer longer option strings. If no-E or --encodingoption is given, initdb attempts todetermine the appropriate encoding to use based on the specified ordefault locale.

You can specify a non-default encoding at database creationtime, provided that the encoding is compatible with the selectedlocale:

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:

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 ofthe source database, because that might result in corrupt data. Formore information see Section21.3.

The encoding for a database is stored in the system catalogpg_database. You can see it by using thepsql-l option orthe l command.

Important: On most modern operating systems, PostgreSQL can determine which character setis implied by the LC_CTYPE setting, and itwill enforce that only the matching database encoding is used. Onolder systems it is your responsibility to ensure that you use theencoding expected by the locale you have selected. A mistake inthis area is likely to lead to strange behavior of locale-dependentoperations such as sorting.

PostgreSQL will allowsuperusers to create databases with SQL_ASCII encoding even when LC_CTYPE is not C orPOSIX. As noted above, SQL_ASCII does not enforce that the data stored inthe database has any particular encoding, and so this choice posesrisks of locale-dependent misbehavior. Using this combination ofsettings is deprecated and may someday be forbidden altogether.

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22.3.3.Automatic Character Set Conversion Between Server andClient

PostgreSQL supports automaticcharacter set conversion between server and client for certaincharacter set combinations. The conversion information is stored inthe pg_conversion system catalog.PostgreSQL comes with somepredefined conversions, as shown in Table 22-2. Youcan create a new conversion using the SQL command CREATE CONVERSION.

Table 22-2. Client/Server Character Set Conversions

To enable automatic character set conversion, you have to tellPostgreSQL the character set(encoding) you would like to use in the client. There are severalways to accomplish this:

• Using the encoding command inpsql. encoding allows you to change client encoding onthe fly. For example, to change the encoding to SJIS, type:

• libpq (Section 31.10) has functions to controlthe client encoding.

• Using SET client_encoding TO. Settingthe client encoding can be done with this SQL command:

  Also you can use the standard SQL syntax SETNAMES for this purpose:

  To query the current client encoding:

  To return to the default encoding:

• Using PGCLIENTENCODING. If theenvironment variable PGCLIENTENCODING isdefined in the client's environment, that client encoding isautomatically selected when a connection to the server is made.(This can subsequently be overridden using any of the other methodsmentioned above.)

• Using the configuration variable client_encoding.If the client_encoding variable is set,that client encoding is automatically selected when a connection tothe server is made. (This can subsequently be overridden using anyof the other methods mentioned above.)

If the conversion of a particular character is not possible —suppose you chose EUC_JP for the serverand LATIN1 for the client, and someJapanese characters are returned that do not have a representationin 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 areworking with all-ASCII data.

22.3.4. FurtherReading

These are good sources to start learning about various kinds ofencoding systems.

Postico 1 3 2 – A Modern Postgresql Client Create Account

Contains detailed explanations of EUC_JP, EUC_CN, EUC_KR, EUC_TW.

The web site of the Unicode Consortium.

UTF-8 (8-bit UCS/UnicodeTransformation Format) is defined here.