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Commit 5b1f92ea authored by Tatsuo Ishii's avatar Tatsuo Ishii
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Update multi-byte support README

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postgresql 6.5.1 multi-byte (MB) support README July 11 1999
PostgreSQL 7.0 multi-byte (MB) support README Mar 22 2000
Tatsuo Ishii
t-ishii@sra.co.jp
ishii@postgresql.org
http://www.sra.co.jp/people/t-ishii/PostgreSQL/
0. Introduction
......@@ -9,12 +9,12 @@ postgresql 6.5.1 multi-byte (MB) support README July 11 1999
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
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 create
database SQL command. So you could have multiple databases with
different encoding systems.
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
......@@ -24,11 +24,11 @@ me know if you find any problem while using 8-bit characters)
1. How to use
run configure with the mb option:
run configure with a multibyte option:
% configure --with-mb=encoding_system
% ./configure --enable-multibyte[=encoding_system]
where encoding_system is one of:
where the encoding_system is one of:
SQL_ASCII ASCII
EUC_JP Japanese EUC
......@@ -48,21 +48,21 @@ where encoding_system is one of:
Example:
% configure --with-mb=EUC_JP
% ./configure --enable-multibyte=EUC_JP
If MB is disabled, nothing is changed except better supporting for
8-bit single byte character sets.
If the encoding system is omitted (./configure --enable-multibyte),
SQL_ASCII is assumed.
2. How to set encoding
2. How to set the encoding
initdb command defines the default encoding for a PostgreSQL
installation. For example:
% initdb -e EUC_JP
% 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
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.
......@@ -75,78 +75,85 @@ 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.
pg_database system catalog. You can see that by using -l or \l of psql
command.
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
$ 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)
A number in the encoding column is "encoding id" and can be translated
to the encoding name using pg_encoding command.
3. Automatic encoding translation between backend and frontend
$ pg_encoding 1
EUC_JP
PostgreSQL supports an automatic encoding translation between backend
and frontend for some encodings.
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.
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
$ pg_encoding EUC_JP
1
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.
3. PGCLIENTENCODING
o using \encoding command in psql
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.
\encoding allows you to change frontend encoding on the fly. For
example, to change the encoding to SJIS, type:
Supported encodings for PGCLIENTENCODING are:
\encoding SJIS
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 Windows CP1251
ALT Windows CP866
WIN1250 Windows CP1250 (Czech)
o using libpq functions
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:
\encoding actually calls PQsetClientEncoding() for its purpose.
(HEXA DECIMAL)
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.
3. SET CLIENT_ENCODING TO command
o using SET CLIENT_ENCODING TO command
Actually setting the frontend side encoding information is done by a
new command:
Setting the frontend side encoding can be done a SQL 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:
Also you can use SQL92 syntax "SET NAMES" for this purpose:
SET NAMES 'encoding';
......@@ -158,10 +165,21 @@ 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. About Unicode
4. References
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.
......@@ -178,6 +196,16 @@ Unicode: http://www.unicode.org/
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)
......
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