22.3. Character Set Support
The character set support in Postgres Pro 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 Postgres Pro 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.
22.3.1. Supported Character Sets
Table 22.1 shows the character sets available for use in Postgres Pro.
Table 22.1. Postgres Pro 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 Postgres Pro 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 Postgres Pro will be unable to help you by converting or validating non-ASCII characters.
22.3.2. Setting the Character Set
initdb
defines the default character set (encoding) for a Postgres Pro 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 21.3.
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, Postgres Pro 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.
Postgres Pro 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.
22.3.3. Automatic Character Set Conversion Between Server and Client
Postgres Pro supports automatic character set conversion between server and client for many combinations of character sets (Section 22.3.4 shows which ones).
To enable automatic character set conversion, you have to tell Postgres Pro 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 toSJIS
, type:\encoding SJIS
libpq (Section 31.10) 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 variablePGCLIENTENCODING
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.
22.3.4. Available Character Set Conversions
Postgres Pro allows conversion between any two character sets for which a conversion function is listed in the pg_conversion
system catalog. Postgres Pro comes with some predefined conversions, as summarized in Table 22.2 and shown in more detail in Table 22.3. 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 22.2. 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 22.3. 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 |
22.3.5. 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.