| The character set support in EnterpriseDB
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 EnterpriseDB 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.
Table 34-1 shows the character sets available
for use in the server.
Table 34-1. Server Character Sets Name | Description |
---|
SQL_ASCII | ASCII | EUC_JP | Japanese EUC | EUC_CN | Chinese EUC | EUC_KR | Korean EUC | JOHAB | Korean EUC (Hangle base) | EUC_TW | Taiwan EUC | UNICODE | Unicode (UTF-8) | MULE_INTERNAL | Mule internal code | LATIN1 | ISO 8859-1/ECMA 94 (Latin alphabet no.1) | LATIN2 | ISO 8859-2/ECMA 94 (Latin alphabet no.2) | LATIN3 | ISO 8859-3/ECMA 94 (Latin alphabet no.3) | LATIN4 | ISO 8859-4/ECMA 94 (Latin alphabet no.4) | LATIN5 | ISO 8859-9/ECMA 128 (Latin alphabet no.5) | LATIN6 | ISO 8859-10/ECMA 144 (Latin alphabet no.6) | LATIN7 | ISO 8859-13 (Latin alphabet no.7) | LATIN8 | ISO 8859-14 (Latin alphabet no.8) | LATIN9 | ISO 8859-15 (Latin alphabet no.9) | LATIN10 | ISO 8859-16/ASRO SR 14111 (Latin alphabet no.10) | ISO_8859_5 | ISO 8859-5/ECMA 113 (Latin/Cyrillic) | ISO_8859_6 | ISO 8859-6/ECMA 114 (Latin/Arabic) | ISO_8859_7 | ISO 8859-7/ECMA 118 (Latin/Greek) | ISO_8859_8 | ISO 8859-8/ECMA 121 (Latin/Hebrew) | KOI8 | KOI8-R(U) | ALT | Windows CP866 | WIN874 | Windows CP874 (Thai) | WIN1250 | Windows CP1250 | WIN | Windows CP1251 | WIN1256 | Windows CP1256 (Arabic) | TCVN | TCVN-5712/Windows CP1258 (Vietnamese) |
Not all APIs support all the listed character sets. For example, the
EnterpriseDB
JDBC driver does not support MULE_INTERNAL, LATIN6,
LATIN8, and LATIN10.
initdb defines the default character set
for a EnterpriseDB 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 gsql.
$ gsql -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)
EnterpriseDB 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. EnterpriseDB comes with some
predefined conversions. They are listed in Table 34-2.
Table 34-2. Client/Server Character Set Conversions Server Character Set | Available Client Character Sets |
---|
SQL_ASCII | SQL_ASCII, UNICODE, MULE_INTERNAL
| EUC_JP | EUC_JP, SJIS,
UNICODE, MULE_INTERNAL
| EUC_CN | EUC_CN, UNICODE, MULE_INTERNAL
| EUC_KR | EUC_KR, UNICODE, MULE_INTERNAL
| JOHAB | JOHAB, UNICODE
| EUC_TW | EUC_TW, BIG5,
UNICODE, MULE_INTERNAL
| LATIN1 | LATIN1, UNICODE
MULE_INTERNAL
| LATIN2 | LATIN2, WIN1250,
UNICODE,
MULE_INTERNAL
| LATIN3 | LATIN3, UNICODE,
MULE_INTERNAL
| LATIN4 | LATIN4, UNICODE,
MULE_INTERNAL
| LATIN5 | LATIN5, UNICODE
| LATIN6 | LATIN6, UNICODE,
MULE_INTERNAL
| LATIN7 | LATIN7, UNICODE,
MULE_INTERNAL
| LATIN8 | LATIN8, UNICODE,
MULE_INTERNAL
| LATIN9 | LATIN9, UNICODE,
MULE_INTERNAL
| LATIN10 | LATIN10, UNICODE,
MULE_INTERNAL
| ISO_8859_5 | ISO_8859_5,
UNICODE,
MULE_INTERNAL,
WIN,
ALT,
KOI8
| ISO_8859_6 | ISO_8859_6,
UNICODE
| ISO_8859_7 | ISO_8859_7,
UNICODE
| ISO_8859_8 | ISO_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_INTERNAL | EUC_JP, SJIS, EUC_KR, EUC_CN,
EUC_TW, BIG5, LATIN1 to LATIN5,
WIN, ALT,
WIN1250,
BIG5, ISO_8859_5, KOI8 | KOI8 | ISO_8859_5, WIN,
ALT, KOI8,
UNICODE, MULE_INTERNAL
| ALT | ISO_8859_5, WIN,
ALT, KOI8,
UNICODE, MULE_INTERNAL
| WIN874 | WIN874,
UNICODE
| WIN1250 | LATIN2, WIN1250,
UNICODE, MULE_INTERNAL
| WIN | ISO_8859_5, WIN,
ALT, KOI8,
UNICODE, MULE_INTERNAL
| WIN1256 | WIN1256,
UNICODE
| TCVN | TCVN,
UNICODE
|
To enable the automatic character set conversion, you have to
tell EnterpriseDB the character set
(encoding) you would like to use in the client. There are several
ways to accomplish this:
Using the \encoding command in
gsql.
\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 more 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 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 cannot be converted to
LATIN1 - it is transformed to its
hexadecimal byte values in parentheses, e.g.,
(826C).
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.
| |
---|