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postgresql/doc/README.mb
Tatsuo Ishii aa387054d2 Multibyte documentations update
2000-05-20 13:40:13 +00:00

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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
May 20, 2000
* SJIS UDC (NEC selection IBM kanji) support contributed
by Eiji Tokuya
* Changes above will appear in 7.0.1
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
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