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postgresql/doc/README.mb
Tatsuo Ishii 6a8d4822ef Document updation for 6.5
1999-04-13 09:29:46 +00:00

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postgresql 6.5 multi-byte (MB) support README Mar 23 1999
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 default
encoding system chosen is determined while initializing your
PostgreSQL installation using initdb(1). Note that this can be
overridden when you create a database using createdb(1) or create
database SQL command. So you could have multiple databases with
different encoding systems.
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
run configure with the mb option:
% configure --with-mb=encoding_system
where encoding_system is one of:
SQL_ASCII ASCII
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 languages
LATIN2 ISO 8859-2 English and some European languages
LATIN3 ISO 8859-3 English and some European languages
LATIN4 ISO 8859-4 English and some European languages
LATIN5 ISO 8859-5 English and some European languages
KOI8 KOI8-R
WIN CP1251
ALT CP866
Example:
% configure --with-mb=EUC_JP
If MB is disabled, nothing is changed except better supporting for
8-bit single byte character sets.
2. How to set encoding
initdb command defines the default encoding for a PostgreSQL
installation. For example:
% initdb -e EUC_JP
sets the default encoding to EUC_JP(Extended Unix Code for Japanese).
Note that you can use "-pgencoding" instead of "-e" if you like longer
option string:-) If no -e or -pgencoding option is given, the encoding
specified at the compile time is used.
You can create a database with a different encoding.
% createdb -E EUC_KR korean
will create a database named "korean" with EUC_KR encoding. The
another way to accomplish this is to use a SQL command:
CREATE DATABASE korean WITH ENCODING = 'EUC_KR';
The encoding for a database is represented as "encoding" column in the
pg_database system catalog.
datname |datdba|encoding|datpath
-------------+------+--------+-------------
template1 | 1739| 1|template1
postgres | 1739| 0|postgres
euc_jp | 1739| 1|euc_jp
euc_kr | 1739| 3|euc_kr
euc_cn | 1739| 2|euc_cn
unicode | 1739| 5|unicode
mule_internal| 1739| 6|mule_internal
A number in the encoding column is "encoding id" and can be translated
to the encoding name using pg_encoding command.
$ pg_encoding 1
EUC_JP
If an argument to pg_encoding is not a number, then it is regarded as
an encoding name and pg_encoding will return the encoding id.
$ pg_encoding EUC_JP
1
3. 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:
SQL_ASCII ASCII
EUC_JP Japanese EUC
SJIS Yet another Japanese encoding
EUC_CN Chinese EUC
EUC_KR Korean EUC
EUC_TW Taiwan EUC
BIG5 Traditional Chinese
MULE_INTERNAL Mule internal
LATIN1 ISO 8859-1 English and some European languages
LATIN2 ISO 8859-2 English and some European languages
LATIN3 ISO 8859-3 English and some European languages
LATIN4 ISO 8859-4 English and some European languages
LATIN5 ISO 8859-5 English and some European languages
KOI8 KOI8-R
WIN CP1251
ALT CP866
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 frontend, 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. Also you can use SQL92 syntax "SET NAMES" for this
purpose:
SET NAMES 'encoding';
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 encoding 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
Mar 23, 1999
* Add support for KOI8(KOI8-R), WIN(CP1251), ALT(CP866)
(thanks Oleg Broytmann for testing)
* Fix problem with MB and locale
Jan 26, 1999
* Add support for Big5 for fronend encoding
(you need to create a database with EUC_TW to use Big5)
* Add regression test case for EUC_TW
(contributed by Jonah Kuo <jonahkuo@mail.ttn.com.tw>)
Dec 15, 1998
* Bugs related to SQL_ASCII support fixed
Nov 5, 1998
* 6.4 release. In this version, pg_database has "encoding"
column that represents the database encoding
Jul 22, 1998
* determine encoding at initdb/createdb rather than compile time
* support for PGCLIENTENCODING when issuing COPY command
* support for SQL92 syntax "SET NAMES"
* support for LATIN2-5
* add UNICODE regression test case
* new test suite for MB
* clean up source files
Jun 5, 1998
* 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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