postgresql/doc/README.mb

PostgreSQL 7.0 multi-byte (MB) support README	  Mar 22 2000

						Tatsuo Ishii
						ishii@postgresql.org
		  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 other 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 by using a
create database SQL command. So you could have multiple databases with
each 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 a multibyte option:

	% ./configure --enable-multibyte[=encoding_system]

where the 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			Windows CP1251
	ALT			Windows CP866

Example:

	% ./configure --enable-multibyte=EUC_JP

If the encoding system is omitted (./configure --enable-multibyte),
SQL_ASCII is assumed.

2. How to set the 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 "--encoding" instead of "-E" if you like longer
option string:-) If no -E or --encoding 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. You can see that by using -l or \l of psql
command.

$ psql -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)

3. Automatic encoding translation between backend and frontend

PostgreSQL supports an automatic encoding translation between backend
and frontend for some encodings.

  encoding of backend			available encoding of frontend
  --------------------------------------------------------------------
	EUC_JP				EUC_JP, SJIS
  
	EUC_TW				EUC_TW, BIG5
  
  	LATIN2				LATIN2, WIN1250
  
	LATIN5				LATIN5, WIN, ALT
  
	MULE_INTERNAL			EUC_JP, SJIS, EUC_KR, EUC_CN, 
					EUC_TW, BIG5, LATIN1 to LATIN5, 
					WIN, ALT, WIN1250

To enable the automatic encoding translation, you have to tell
PostgreSQL the encoding you would like to use in frontend. There are
several ways to accomplish this.

o using \encoding command in psql

\encoding allows you to change frontend encoding on the fly. For
example, to change the encoding to SJIS, type:

	\encoding SJIS

o using libpq functions

\encoding actually calls PQsetClientEncoding() for its purpose.

  int PQsetClientEncoding(PGconn *conn, const char *encoding)

conn is a connection to the backend, and encoding is an encoding you
want to use. If it successfully sets the encoding, it returns 0,
otherwise -1. The current encoding for this connection can be shown by
using:

  int PQclientEncoding(const PGconn *conn)

Note that it returns the "encoding id," not the encoding symbol string
such as "EUC_JP." To convert an encoding id to an encoding symbol, you
can use:

char *pg_encoding_to_char(int encoding_id)

o using PGCLIENTENCODING

If an environment variable PGCLIENTENCODING is defined in the
frontend, an automatic encoding translation is done by the backend.

o using SET CLIENT_ENCODING TO command

Setting the frontend side encoding can be done a SQL command:

	SET CLIENT_ENCODING TO 'encoding';

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;

4. About Unicode

An automatic encoding translation between Unicode and any other
encodings is not supported (yet). 

5. What happens if the translation is not possible?

Suppose you choose EUC_JP for the backend, LATIN1 for the frontend,
then some Japanese characters could not be translated into LATIN1. In
this case, a letter cannot be represented in the LATIN1 character set,
would be transformed as:

	(HEXA DECIMAL)

6. 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 22, 2000
	* Add new libpq functions PQsetClientEncoding, PQclientEncoding
	* ./configure --with-mb=EUC_JP
	  now deprecated. use 
	  ./configure --enable-multibyte=EUC_JP
	  instead
  	* Add SQL_ASCII regression test case
	* Add SJIS User Defined Character (UDC) support
	* All of above will appear in 7.0

July 11, 1999
	* Add support for WIN1250 (Windows Czech) as a client encoding
	  (contributed by Pavel Behal)
	* fix some compiler warnings (contributed by Tomoaki Nishiyama)

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

Appendix:

[Here is a good documentation explaining how to use WIN1250 on
Windows/ODBC from Pavel Behal. Please note that Installation step 1)
is not necceary in 6.5.1 -- Tatsuo]

Version: 0.91 for PgSQL 6.5
Author: Pavel Behal
Revised by: Tatsuo Ishii
Email: behal@opf.slu.cz
Licence: The Same as PostgreSQL

Sorry for my Eglish and C code, I'm not native :-)

!!!!!!!!!!!!!!!!!!!!!!!!! NO WARRANTY !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Instalation:
------------
1) Change three affected files in source directories 
    (I don't have time to create proper patch diffs, I don't know how)
2) Compile with enabled locale and multibyte set to LATIN2
3) Setup properly your instalation, do not forget to create locale
   variables in your profile (environment). Ex. (may not be exactly true):
	LC_ALL=cs_CZ.ISO8859-2
	LC_COLLATE=cs_CZ.ISO8859-2
	LC_CTYPE=cs_CZ.ISO8859-2
	LC_MONETARY=cs_CZ.ISO8859-2
	LC_NUMERIC=cs_CZ.ISO8859-2
	LC_TIME=cs_CZ.ISO8859-2
4) You have to start the postmaster with locales set!
5) Try it with Czech language, it have to sort
5) Install ODBC driver for PgSQL into your M$ Windows
6) Setup properly your data source. Include this line in your ODBC
   configuration dialog in field "Connect Settings:" :
	SET CLIENT_ENCODING = 'WIN1250';
7) Now try it again, but in Windows with ODBC.

Description:
------------
- Depends on proper system locales, tested with RH6.0 and Slackware 3.6,
  with cs_CZ.iso8859-2 loacle
- Never try to set-up server multibyte database encoding to WIN1250,
  always use LATIN2 instead. There is not WIN1250 locale in Unix
- WIN1250 encoding is useable only for M$W ODBC clients. The characters are
  on thy fly re-coded, to be displayed and stored back properly
 
Important:
----------
- it reorders your sort order depending on your LC_... setting, so don't be
  confused with regression tests, they don't use locale
- "ch" is corectly sorted only in some newer locales (Ex. RH6.0)
- you have to insert money as '162,50' (with comma in aphostrophes!)
- not tested properly