PostgreSQL

PostgreSQL Elephant Logo

23.3. Character Set Support

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 libc-provided locales there is only one character set that will work correctly. (On Windows, however, UTF-8 encoding can be used with any locale.) If you have ICU support configured, ICU-provided locales can be used with most but not all server-side encodings.

23.3.1. Supported Character Sets

Table 23.1 shows the character sets available for use in PostgreSQL.

Table 23.1. PostgreSQL Character Sets

Name Description Language Server? ICU? Bytes/Char Aliases

BIG5

Big Five

Traditional Chinese

No

No

1-2

WIN950, Windows950

EUC_CN

Extended UNIX Code-CN

Simplified Chinese

Yes

Yes

1-3

EUC_JP

Extended UNIX Code-JP

Japanese

Yes

Yes

1-3

EUC_JIS_2004

Extended UNIX Code-JP, JIS X 0213

Japanese

Yes

No

1-3

EUC_KR

Extended UNIX Code-KR

Korean

Yes

Yes

1-3

EUC_TW

Extended UNIX Code-TW

Traditional Chinese, Taiwanese

Yes

Yes

1-3

GB18030

National Standard

Chinese

No

No

1-4

GBK

Extended National Standard

Simplified Chinese

No

No

1-2

WIN936, Windows936

ISO_8859_5

ISO 8859-5, ECMA 113

Latin/Cyrillic

Yes

Yes

1

ISO_8859_6

ISO 8859-6, ECMA 114

Latin/Arabic

Yes

Yes

1

ISO_8859_7

ISO 8859-7, ECMA 118

Latin/Greek

Yes

Yes

1

ISO_8859_8

ISO 8859-8, ECMA 121

Latin/Hebrew

Yes

Yes

1

JOHAB

JOHAB

Korean (Hangul)

No

No

1-3

KOI8R

KOI8-R

Cyrillic (Russian)

Yes

Yes

1

KOI8

KOI8U

KOI8-U

Cyrillic (Ukrainian)

Yes

Yes

1

LATIN1

ISO 8859-1, ECMA 94

Western European

Yes

Yes

1

ISO88591

LATIN2

ISO 8859-2, ECMA 94

Central European

Yes

Yes

1

ISO88592

LATIN3

ISO 8859-3, ECMA 94

South European

Yes

Yes

1

ISO88593

LATIN4

ISO 8859-4, ECMA 94

North European

Yes

Yes

1

ISO88594

LATIN5

ISO 8859-9, ECMA 128

Turkish

Yes

Yes

1

ISO88599

LATIN6

ISO 8859-10, ECMA 144

Nordic

Yes

Yes

1

ISO885910

LATIN7

ISO 8859-13

Baltic

Yes

Yes

1

ISO885913

LATIN8

ISO 8859-14

Celtic

Yes

Yes

1

ISO885914

LATIN9

ISO 8859-15

LATIN1 with Euro and accents

Yes

Yes

1

ISO885915

LATIN10

ISO 8859-16, ASRO SR 14111

Romanian

Yes

No

1

ISO885916

MULE_INTERNAL

Mule internal code

Multilingual Emacs

Yes

No

1-4

SJIS

Shift JIS

Japanese

No

No

1-2

Mskanji, ShiftJIS, WIN932, Windows932

SHIFT_JIS_2004

Shift JIS, JIS X 0213

Japanese

No

No

1-2

SQL_ASCII

unspecified (see text)

any

Yes

No

1

UHC

Unified Hangul Code

Korean

No

No

1-2

WIN949, Windows949

UTF8

Unicode, 8-bit

all

Yes

Yes

1-4

Unicode

WIN866

Windows CP866

Cyrillic

Yes

Yes

1

ALT

WIN874

Windows CP874

Thai

Yes

No

1

WIN1250

Windows CP1250

Central European

Yes

Yes

1

WIN1251

Windows CP1251

Cyrillic

Yes

Yes

1

WIN

WIN1252

Windows CP1252

Western European

Yes

Yes

1

WIN1253

Windows CP1253

Greek

Yes

Yes

1

WIN1254

Windows CP1254

Turkish

Yes

Yes

1

WIN1255

Windows CP1255

Hebrew

Yes

Yes

1

WIN1256

Windows CP1256

Arabic

Yes

Yes

1

WIN1257

Windows CP1257

Baltic

Yes

Yes

1

WIN1258

Windows CP1258

Vietnamese

Yes

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.

23.3.2. Setting the Character Set

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 Section 22.3.

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)

Important

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.

23.3.3. 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 23.2. You can create a new conversion using the SQL command CREATE CONVERSION.

Table 23.2. 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_JIS_2004

EUC_JIS_2004, SHIFT_JIS_2004, 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

not supported as a server encoding

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

SHIFT_JIS_2004

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 (Section 34.10) 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 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, 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.

23.3.4. Further Reading

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.

http://www.unicode.org/

The web site of the Unicode Consortium.

RFC 3629

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


Prev Up Next

23.2. Collation Support

Home

Chapter 24. Routine Database Maintenance Tasks

Copyright © 1996-2023 The PostgreSQL Global Development Group