20.2. 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), Unicode, 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.

20.2.1. Supported Character Sets

Table 20-1 shows the character sets available for use in the server.

Table 20-1. Server Character Sets

NameDescription
SQL_ASCIIASCII
EUC_JPJapanese EUC
EUC_CNChinese EUC
EUC_KRKorean EUC
JOHABKorean EUC (Hangle base)
EUC_TWTaiwan EUC
UNICODEUnicode (UTF-8)
MULE_INTERNALMule internal code
LATIN1ISO 8859-1/ECMA 94 (Latin alphabet no.1)
LATIN2ISO 8859-2/ECMA 94 (Latin alphabet no.2)
LATIN3ISO 8859-3/ECMA 94 (Latin alphabet no.3)
LATIN4ISO 8859-4/ECMA 94 (Latin alphabet no.4)
LATIN5ISO 8859-9/ECMA 128 (Latin alphabet no.5)
LATIN6ISO 8859-10/ECMA 144 (Latin alphabet no.6)
LATIN7ISO 8859-13 (Latin alphabet no.7)
LATIN8ISO 8859-14 (Latin alphabet no.8)
LATIN9ISO 8859-15 (Latin alphabet no.9)
LATIN10ISO 8859-16/ASRO SR 14111 (Latin alphabet no.10)
ISO_8859_5ISO 8859-5/ECMA 113 (Latin/Cyrillic)
ISO_8859_6ISO 8859-6/ECMA 114 (Latin/Arabic)
ISO_8859_7ISO 8859-7/ECMA 118 (Latin/Greek)
ISO_8859_8ISO 8859-8/ECMA 121 (Latin/Hebrew)
KOI8KOI8-R(U)
WINWindows CP1251
ALTWindows CP866
WIN1256Windows CP1256 (Arabic)
TCVNTCVN-5712/Windows CP1258 (Vietnamese)
WIN874Windows CP874 (Thai)

Important: Before PostgreSQL 7.2, LATIN5 mistakenly meant ISO 8859-5. From 7.2 on, LATIN5 means ISO 8859-9. If you have a LATIN5 database created on 7.1 or earlier and want to migrate to 7.2 or later, you should be careful about this change.

Not all APIs support all the listed character sets. For example, the PostgreSQL JDBC driver does not support MULE_INTERNAL, LATIN6, LATIN8, and LATIN10.

20.2.2. 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, SQL_ASCII is used.

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
 regression    | t-ishii | SQL_ASCII
 template1     | t-ishii | EUC_JP
 test          | t-ishii | EUC_JP
 unicode       | t-ishii | UNICODE
(9 rows)

20.2.3. Automatic Character Set Conversion Between Server and Client

PostgreSQL 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 Table 20-2.

Table 20-2. Client/Server Character Set Conversions

Server Character SetAvailable Client Character Sets
SQL_ASCIISQL_ASCII, UNICODE, MULE_INTERNAL
EUC_JPEUC_JP, SJIS, UNICODE, MULE_INTERNAL
EUC_CNEUC_CN, UNICODE, MULE_INTERNAL
EUC_KREUC_KR, UNICODE, MULE_INTERNAL
JOHABJOHAB, UNICODE
EUC_TWEUC_TW, BIG5, UNICODE, MULE_INTERNAL
LATIN1LATIN1, UNICODE MULE_INTERNAL
LATIN2LATIN2, WIN1250, UNICODE, MULE_INTERNAL
LATIN3LATIN3, UNICODE, MULE_INTERNAL
LATIN4LATIN4, UNICODE, MULE_INTERNAL
LATIN5LATIN5, UNICODE
LATIN6LATIN6, UNICODE, MULE_INTERNAL
LATIN7LATIN7, UNICODE, MULE_INTERNAL
LATIN8LATIN8, UNICODE, MULE_INTERNAL
LATIN9LATIN9, UNICODE, MULE_INTERNAL
LATIN10LATIN10, UNICODE, MULE_INTERNAL
ISO_8859_5ISO_8859_5, UNICODE, MULE_INTERNAL, WIN, ALT, KOI8
ISO_8859_6ISO_8859_6, UNICODE
ISO_8859_7ISO_8859_7, UNICODE
ISO_8859_8ISO_8859_8, UNICODE
UNICODE EUC_JP, SJIS, EUC_KR, UHC, JOHAB, EUC_CN, GBK, EUC_TW, BIG5, LATIN1 to LATIN10, ISO_8859_5, ISO_8859_6, ISO_8859_7, ISO_8859_8, WIN, ALT, KOI8, WIN1256, TCVN, WIN874, GB18030, WIN1250
MULE_INTERNALEUC_JP, SJIS, EUC_KR, EUC_CN, EUC_TW, BIG5, LATIN1 to LATIN5, WIN, ALT, WIN1250, BIG5, ISO_8859_5, KOI8
KOI8ISO_8859_5, WIN, ALT, KOI8, UNICODE, MULE_INTERNAL
WINISO_8859_5, WIN, ALT, KOI8, UNICODE, MULE_INTERNAL
ALTISO_8859_5, WIN, ALT, KOI8, UNICODE, MULE_INTERNAL
WIN1256WIN1256, UNICODE
TCVNTCVN, UNICODE
WIN874WIN874, UNICODE

To enable the 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:

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).

20.2.4. Further Reading

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

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.

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