postgres/doc/README.mb

postgresql 6.5 multi-byte (MB) support README	  Jan 26 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 encoding system
chosen is determined when initializing your PostgreSQL installation
using initdb(1). Note that this can be overridden when creating a
database using createdb(1) or create database SQL command. So you
could have multiple databases with different encoding system.

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

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

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. 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 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

Jan 26, 1999
	* Add support 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