Supported Versions: Current (16) / 15 / 14 / 13 / 12
Development Versions: devel
Unsupported versions: 11 / 10 / 9.6 / 9.5 / 9.4 / 9.3 / 9.2 / 9.1 / 9.0 / 8.4 / 8.3 / 8.2 / 8.1 / 8.0 / 7.4 / 7.3 / 7.2 / 7.1
This documentation is for an unsupported version of PostgreSQL.
You may want to view the same page for the current version, or one of the other supported versions listed above instead.

21.2. Character Set Support

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 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.

21.2.1. Supported Character Sets

Table 21-1 shows the character sets available for use in PostgreSQL.

Table 21-1. PostgreSQL Character Sets

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_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 1-2  
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) Yes 1-3  
KOI8 KOI8-R(U) Cyrillic Yes 1 KOI8R
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
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  
WIN1256 Windows CP1256 Arabic Yes 1  
WIN1258 Windows CP1258 Vietnamese Yes 1 ABC, TCVN, TCVN5712, VSCII

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.

21.2.2. Setting the Character Set

initdb 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 --encoding instead of -E if you prefer to type 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 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 -l 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)

Important: 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.

21.2.3. Automatic Character Set Conversion Between Server and Client

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 Table 21-2. You can create a new conversion using the SQL command CREATE CONVERSION.

Table 21-2. Client/Server Character Set Conversions

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, KOI8, 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
KOI8 KOI8, ISO_8859_5, MULE_INTERNAL, UTF8, WIN866, WIN1251
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, KOI8, 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, KOI8, MULE_INTERNAL, UTF8, WIN1251
WIN874 WIN874, UTF8
WIN1250 WIN1250, LATIN2, MULE_INTERNAL, UTF8
WIN1251 WIN1251, ISO_8859_5, KOI8, MULE_INTERNAL, UTF8, WIN866
WIN1252 WIN1252, UTF8
WIN1256 WIN1256, 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
    
  • 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 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 client_encoding. 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 do not have a representation in LATIN1 — then 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.

21.2.4. Further Reading

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

http://www.i18ngurus.com/docs/984813247.html

An extensive collection of documents about character sets, encodings, and code pages.

ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf

Detailed explanations of EUC_JP, EUC_CN, EUC_KR, EUC_TW appear in section 3.2.

http://www.unicode.org/

The web site of the Unicode Consortium

RFC 2044

UTF-8 is defined here.