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postgresql 6.4 multi-byte (MB) support README Jun 5 1998
Tatsuo Ishii
t-ishii@sra.co.jp
http://www.sra.co.jp/people/t-ishii/PostgreSQL/
0. Introduction
The MB support is intended for allowing PostgreSQL to handle
multi-byte character sets such as EUC(Extended Unix Code), Unicode and
Mule internal code. With the MB enabled you can use multi-byte
character sets in regexp ,LIKE and some functions. The encoding system
chosen is determined at the compile time.
MB also fixes some problems concerning with 8-bit single byte
character sets including ISO8859. (I would not say all of problems
have been fixed. I just confirmed that the regression test ran fine
and a few French characters could be used with the patch. Please let
me know if you find any problem while using 8-bit characters)
1. How to use
create src/Makefile.custom with a line including:
MB=encoding_system
or run configure with the mb option:
% configure --with-mb=encoding_system
where encoding_system is one of:
EUC_JP Japanese EUC
EUC_CN Chinese EUC
EUC_KR Korean EUC
EUC_TW Taiwan EUC
UNICODE Unicode(UTF-8)
MULE_INTERNAL Mule internal
LATIN1 ISO 8859-1 English and some European laguages
Example:
% cat Makefile.custom
MB=EUC_JP
or
% configure --with-mb=EUC_JP
If MB is disabled, nothing is changed except better supporting for
8-bit single byte character sets.
2. PGCLIENTENCODING
If an environment variable PGCLIENTENCODING is defined on the
frontend, automatic encoding translation is done by the backend. For
example, if the backend has been compiled with MB=EUC_JP and
PGCLIENTENCODING=SJIS(Shift JIS: yet another Japanese encoding
system), then any SJIS strings coming from the frontend would be
translated to EUC_JP before going into the parser. Outputs from the
backend would be translated to SJIS of course.
Supported encodings for PGCLIENTENCODING are:
EUC_JP Japanese EUC
SJIS Yet another Japanese encoding
EUC_CN Chinese EUC
EUC_KR Korean EUC
EUC_TW Taiwan EUC
MULE_INTERNAL Mule internal
LATIN1 ISO 8859-1 English and some European laguages
Note that UNICODE is not supported(yet). Also note that the
translation is not always possible. Suppose you choose EUC_JP for the
backend, LATIN1 for the frotend, then some Japanese characters cannot
be translated into latin. In this case, a letter cannot be represented
in the Latin character set, would be transformed as:
(HEXA DECIMAL)
3. SET CLIENT_ENCODING TO command
Actually setting the frontend side encoding information is done by a
new command:
SET CLIENT_ENCODING TO 'encoding';
where encoding is one of the encodings those can be set to
PGCLIENTENCODING. To query the current the frontend encoding:
SHOW CLIENT_ENCODING;
To return to the default encoding:
RESET CLIENT_ENCODING;
This would reset the frontend encoding to same as the backend
encoding, thus no endoing translation would be performed.
4. References
These are good sources to start learning various kind 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.
Unicode: http://www.unicode.org/
The homepage of UNICODE.
RFC 2044
UTF-8 is defined here.
5. History
Jun 5, 1988
* add support for the encoding translation between the backend
and the frontend
* new command SET CLIENT_ENCODING etc. added
* add support for LATIN1 character set
* enhance 8 bit cleaness
April 21, 1998 some enhancements/fixes
* character_length(), position(), substring() are now aware of
multi-byte characters
* add octet_length()
* add --with-mb option to configure
* new regression tests for EUC_KR
(contributed by "Soonmyung. Hong" <hong@lunaris.hanmesoft.co.kr>)
* add some test cases to the EUC_JP regression test
* fix problem in regress/regress.sh in case of System V
* fix toupper(), tolower() to handle 8bit chars
Mar 25, 1998 MB PL2 is incorporated into PostgreSQL 6.3.1
Mar 10, 1998 PL2 released
* add regression test for EUC_JP, EUC_CN and MULE_INTERNAL
* add an English document (this file)
* fix problems concerning 8-bit single byte characters
Mar 1, 1998 PL1 released
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