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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 many combinations of character sets (Section 23.3.4 shows which ones).

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 33.10) 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. (However, if the server's character set is not SQL_ASCII, the server will still check that incoming data is valid for that encoding; so the net effect is as though the client character set were the same as the server's.) Just as for the server, use of SQL_ASCII is unwise unless you are working with all-ASCII data.

23.3.4. Available Character Set Conversions

PostgreSQL allows conversion between any two character sets for which a conversion function is listed in the pg_conversion system catalog. PostgreSQL comes with some predefined conversions, as summarized in Table 23.2 and shown in more detail in Table 23.3. You can create a new conversion using the SQL command CREATE CONVERSION. (To be used for automatic client/server conversions, a conversion must be marked as default for its character set pair.)

Table 23.2. Built-in 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

Table 23.3. All Built-in Character Set Conversions

Conversion Name [a] Source Encoding Destination Encoding
big5_to_euc_tw BIG5 EUC_TW
big5_to_mic BIG5 MULE_INTERNAL
big5_to_utf8 BIG5 UTF8
euc_cn_to_mic EUC_CN MULE_INTERNAL
euc_cn_to_utf8 EUC_CN UTF8
euc_jp_to_mic EUC_JP MULE_INTERNAL
euc_jp_to_sjis EUC_JP SJIS
euc_jp_to_utf8 EUC_JP UTF8
euc_kr_to_mic EUC_KR MULE_INTERNAL
euc_kr_to_utf8 EUC_KR UTF8
euc_tw_to_big5 EUC_TW BIG5
euc_tw_to_mic EUC_TW MULE_INTERNAL
euc_tw_to_utf8 EUC_TW UTF8
gb18030_to_utf8 GB18030 UTF8
gbk_to_utf8 GBK UTF8
iso_8859_10_to_utf8 LATIN6 UTF8
iso_8859_13_to_utf8 LATIN7 UTF8
iso_8859_14_to_utf8 LATIN8 UTF8
iso_8859_15_to_utf8 LATIN9 UTF8
iso_8859_16_to_utf8 LATIN10 UTF8
iso_8859_1_to_mic LATIN1 MULE_INTERNAL
iso_8859_1_to_utf8 LATIN1 UTF8
iso_8859_2_to_mic LATIN2 MULE_INTERNAL
iso_8859_2_to_utf8 LATIN2 UTF8
iso_8859_2_to_windows_1250 LATIN2 WIN1250
iso_8859_3_to_mic LATIN3 MULE_INTERNAL
iso_8859_3_to_utf8 LATIN3 UTF8
iso_8859_4_to_mic LATIN4 MULE_INTERNAL
iso_8859_4_to_utf8 LATIN4 UTF8
iso_8859_5_to_koi8_r ISO_8859_5 KOI8R
iso_8859_5_to_mic ISO_8859_5 MULE_INTERNAL
iso_8859_5_to_utf8 ISO_8859_5 UTF8
iso_8859_5_to_windows_1251 ISO_8859_5 WIN1251
iso_8859_5_to_windows_866 ISO_8859_5 WIN866
iso_8859_6_to_utf8 ISO_8859_6 UTF8
iso_8859_7_to_utf8 ISO_8859_7 UTF8
iso_8859_8_to_utf8 ISO_8859_8 UTF8
iso_8859_9_to_utf8 LATIN5 UTF8
johab_to_utf8 JOHAB UTF8
koi8_r_to_iso_8859_5 KOI8R ISO_8859_5
koi8_r_to_mic KOI8R MULE_INTERNAL
koi8_r_to_utf8 KOI8R UTF8
koi8_r_to_windows_1251 KOI8R WIN1251
koi8_r_to_windows_866 KOI8R WIN866
koi8_u_to_utf8 KOI8U UTF8
mic_to_big5 MULE_INTERNAL BIG5
mic_to_euc_cn MULE_INTERNAL EUC_CN
mic_to_euc_jp MULE_INTERNAL EUC_JP
mic_to_euc_kr MULE_INTERNAL EUC_KR
mic_to_euc_tw MULE_INTERNAL EUC_TW
mic_to_iso_8859_1 MULE_INTERNAL LATIN1
mic_to_iso_8859_2 MULE_INTERNAL LATIN2
mic_to_iso_8859_3 MULE_INTERNAL LATIN3
mic_to_iso_8859_4 MULE_INTERNAL LATIN4
mic_to_iso_8859_5 MULE_INTERNAL ISO_8859_5
mic_to_koi8_r MULE_INTERNAL KOI8R
mic_to_sjis MULE_INTERNAL SJIS
mic_to_windows_1250 MULE_INTERNAL WIN1250
mic_to_windows_1251 MULE_INTERNAL WIN1251
mic_to_windows_866 MULE_INTERNAL WIN866
sjis_to_euc_jp SJIS EUC_JP
sjis_to_mic SJIS MULE_INTERNAL
sjis_to_utf8 SJIS UTF8
windows_1258_to_utf8 WIN1258 UTF8
uhc_to_utf8 UHC UTF8
utf8_to_big5 UTF8 BIG5
utf8_to_euc_cn UTF8 EUC_CN
utf8_to_euc_jp UTF8 EUC_JP
utf8_to_euc_kr UTF8 EUC_KR
utf8_to_euc_tw UTF8 EUC_TW
utf8_to_gb18030 UTF8 GB18030
utf8_to_gbk UTF8 GBK
utf8_to_iso_8859_1 UTF8 LATIN1
utf8_to_iso_8859_10 UTF8 LATIN6
utf8_to_iso_8859_13 UTF8 LATIN7
utf8_to_iso_8859_14 UTF8 LATIN8
utf8_to_iso_8859_15 UTF8 LATIN9
utf8_to_iso_8859_16 UTF8 LATIN10
utf8_to_iso_8859_2 UTF8 LATIN2
utf8_to_iso_8859_3 UTF8 LATIN3
utf8_to_iso_8859_4 UTF8 LATIN4
utf8_to_iso_8859_5 UTF8 ISO_8859_5
utf8_to_iso_8859_6 UTF8 ISO_8859_6
utf8_to_iso_8859_7 UTF8 ISO_8859_7
utf8_to_iso_8859_8 UTF8 ISO_8859_8
utf8_to_iso_8859_9 UTF8 LATIN5
utf8_to_johab UTF8 JOHAB
utf8_to_koi8_r UTF8 KOI8R
utf8_to_koi8_u UTF8 KOI8U
utf8_to_sjis UTF8 SJIS
utf8_to_windows_1258 UTF8 WIN1258
utf8_to_uhc UTF8 UHC
utf8_to_windows_1250 UTF8 WIN1250
utf8_to_windows_1251 UTF8 WIN1251
utf8_to_windows_1252 UTF8 WIN1252
utf8_to_windows_1253 UTF8 WIN1253
utf8_to_windows_1254 UTF8 WIN1254
utf8_to_windows_1255 UTF8 WIN1255
utf8_to_windows_1256 UTF8 WIN1256
utf8_to_windows_1257 UTF8 WIN1257
utf8_to_windows_866 UTF8 WIN866
utf8_to_windows_874 UTF8 WIN874
windows_1250_to_iso_8859_2 WIN1250 LATIN2
windows_1250_to_mic WIN1250 MULE_INTERNAL
windows_1250_to_utf8 WIN1250 UTF8
windows_1251_to_iso_8859_5 WIN1251 ISO_8859_5
windows_1251_to_koi8_r WIN1251 KOI8R
windows_1251_to_mic WIN1251 MULE_INTERNAL
windows_1251_to_utf8 WIN1251 UTF8
windows_1251_to_windows_866 WIN1251 WIN866
windows_1252_to_utf8 WIN1252 UTF8
windows_1256_to_utf8 WIN1256 UTF8
windows_866_to_iso_8859_5 WIN866 ISO_8859_5
windows_866_to_koi8_r WIN866 KOI8R
windows_866_to_mic WIN866 MULE_INTERNAL
windows_866_to_utf8 WIN866 UTF8
windows_866_to_windows_1251 WIN866 WIN
windows_874_to_utf8 WIN874 UTF8
euc_jis_2004_to_utf8 EUC_JIS_2004 UTF8
utf8_to_euc_jis_2004 UTF8 EUC_JIS_2004
shift_jis_2004_to_utf8 SHIFT_JIS_2004 UTF8
utf8_to_shift_jis_2004 UTF8 SHIFT_JIS_2004
euc_jis_2004_to_shift_jis_2004 EUC_JIS_2004 SHIFT_JIS_2004
shift_jis_2004_to_euc_jis_2004 SHIFT_JIS_2004 EUC_JIS_2004

[a] The conversion names follow a standard naming scheme: The official name of the source encoding with all non-alphanumeric characters replaced by underscores, followed by _to_, followed by the similarly processed destination encoding name. Therefore, these names sometimes deviate from the customary encoding names shown in Table 23.1.


23.3.5. 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.

https://www.unicode.org/

The web site of the Unicode Consortium.

RFC 3629

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