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233 lines
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233 lines
7.1 KiB
Plaintext
postgresql 6.5 multi-byte (MB) support README Mar 23 1999
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Tatsuo Ishii
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t-ishii@sra.co.jp
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http://www.sra.co.jp/people/t-ishii/PostgreSQL/
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0. Introduction
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The MB support is intended for allowing PostgreSQL to handle
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multi-byte character sets such as EUC(Extended Unix Code), Unicode and
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Mule internal code. With the MB enabled you can use multi-byte
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character sets in regexp ,LIKE and some functions. The default
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encoding system chosen is determined while initializing your
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PostgreSQL installation using initdb(1). Note that this can be
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overridden when you create a database using createdb(1) or create
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database SQL command. So you could have multiple databases with
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different encoding systems.
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MB also fixes some problems concerning with 8-bit single byte
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character sets including ISO8859. (I would not say all of problems
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have been fixed. I just confirmed that the regression test ran fine
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and a few French characters could be used with the patch. Please let
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me know if you find any problem while using 8-bit characters)
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1. How to use
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run configure with the mb option:
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% configure --with-mb=encoding_system
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where encoding_system is one of:
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SQL_ASCII ASCII
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EUC_JP Japanese EUC
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EUC_CN Chinese EUC
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EUC_KR Korean EUC
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EUC_TW Taiwan EUC
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UNICODE Unicode(UTF-8)
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MULE_INTERNAL Mule internal
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LATIN1 ISO 8859-1 English and some European languages
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LATIN2 ISO 8859-2 English and some European languages
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LATIN3 ISO 8859-3 English and some European languages
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LATIN4 ISO 8859-4 English and some European languages
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LATIN5 ISO 8859-5 English and some European languages
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KOI8 KOI8-R
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WIN CP1251
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ALT CP866
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Example:
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% configure --with-mb=EUC_JP
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If MB is disabled, nothing is changed except better supporting for
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8-bit single byte character sets.
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2. How to set encoding
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initdb command defines the default encoding for a PostgreSQL
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installation. For example:
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% initdb -e EUC_JP
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sets the default encoding to EUC_JP(Extended Unix Code for Japanese).
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Note that you can use "-pgencoding" instead of "-e" if you like longer
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option string:-) If no -e or -pgencoding option is given, the encoding
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specified at the compile time is used.
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You can create a database with a different encoding.
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% createdb -E EUC_KR korean
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will create a database named "korean" with EUC_KR encoding. The
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another way to accomplish this is to use a SQL command:
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CREATE DATABASE korean WITH ENCODING = 'EUC_KR';
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The encoding for a database is represented as "encoding" column in the
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pg_database system catalog.
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datname |datdba|encoding|datpath
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-------------+------+--------+-------------
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template1 | 1739| 1|template1
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postgres | 1739| 0|postgres
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euc_jp | 1739| 1|euc_jp
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euc_kr | 1739| 3|euc_kr
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euc_cn | 1739| 2|euc_cn
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unicode | 1739| 5|unicode
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mule_internal| 1739| 6|mule_internal
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A number in the encoding column is "encoding id" and can be translated
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to the encoding name using pg_encoding command.
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$ pg_encoding 1
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EUC_JP
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If an argument to pg_encoding is not a number, then it is regarded as
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an encoding name and pg_encoding will return the encoding id.
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$ pg_encoding EUC_JP
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1
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3. PGCLIENTENCODING
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If an environment variable PGCLIENTENCODING is defined on the
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frontend, automatic encoding translation is done by the backend. For
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example, if the backend has been compiled with MB=EUC_JP and
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PGCLIENTENCODING=SJIS(Shift JIS: yet another Japanese encoding
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system), then any SJIS strings coming from the frontend would be
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translated to EUC_JP before going into the parser. Outputs from the
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backend would be translated to SJIS of course.
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Supported encodings for PGCLIENTENCODING are:
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SQL_ASCII ASCII
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EUC_JP Japanese EUC
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SJIS Yet another Japanese encoding
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EUC_CN Chinese EUC
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EUC_KR Korean EUC
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EUC_TW Taiwan EUC
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BIG5 Traditional Chinese
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MULE_INTERNAL Mule internal
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LATIN1 ISO 8859-1 English and some European languages
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LATIN2 ISO 8859-2 English and some European languages
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LATIN3 ISO 8859-3 English and some European languages
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LATIN4 ISO 8859-4 English and some European languages
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LATIN5 ISO 8859-5 English and some European languages
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KOI8 KOI8-R
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WIN CP1251
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ALT CP866
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Note that UNICODE is not supported(yet). Also note that the
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translation is not always possible. Suppose you choose EUC_JP for the
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backend, LATIN1 for the frontend, then some Japanese characters cannot
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be translated into latin. In this case, a letter cannot be represented
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in the Latin character set, would be transformed as:
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(HEXA DECIMAL)
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3. SET CLIENT_ENCODING TO command
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Actually setting the frontend side encoding information is done by a
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new command:
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SET CLIENT_ENCODING TO 'encoding';
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where encoding is one of the encodings those can be set to
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PGCLIENTENCODING. Also you can use SQL92 syntax "SET NAMES" for this
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purpose:
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SET NAMES 'encoding';
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To query the current the frontend encoding:
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SHOW CLIENT_ENCODING;
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To return to the default encoding:
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RESET CLIENT_ENCODING;
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This would reset the frontend encoding to same as the backend
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encoding, thus no encoding translation would be performed.
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4. References
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These are good sources to start learning various kind of encoding
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systems.
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ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf
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Detailed explanations of EUC_JP, EUC_CN, EUC_KR, EUC_TW
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appear in section 3.2.
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Unicode: http://www.unicode.org/
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The homepage of UNICODE.
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RFC 2044
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UTF-8 is defined here.
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5. History
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Mar 23, 1999
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* Add support for KOI8(KOI8-R), WIN(CP1251), ALT(CP866)
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(thanks Oleg Broytmann for testing)
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* Fix problem with MB and locale
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Jan 26, 1999
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* Add support for Big5 for fronend encoding
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(you need to create a database with EUC_TW to use Big5)
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* Add regression test case for EUC_TW
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(contributed by Jonah Kuo <jonahkuo@mail.ttn.com.tw>)
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Dec 15, 1998
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* Bugs related to SQL_ASCII support fixed
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Nov 5, 1998
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* 6.4 release. In this version, pg_database has "encoding"
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column that represents the database encoding
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Jul 22, 1998
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* determine encoding at initdb/createdb rather than compile time
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* support for PGCLIENTENCODING when issuing COPY command
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* support for SQL92 syntax "SET NAMES"
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* support for LATIN2-5
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* add UNICODE regression test case
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* new test suite for MB
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* clean up source files
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Jun 5, 1998
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* add support for the encoding translation between the backend
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and the frontend
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* new command SET CLIENT_ENCODING etc. added
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* add support for LATIN1 character set
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* enhance 8 bit cleaness
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April 21, 1998 some enhancements/fixes
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* character_length(), position(), substring() are now aware of
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multi-byte characters
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* add octet_length()
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* add --with-mb option to configure
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* new regression tests for EUC_KR
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(contributed by "Soonmyung. Hong" <hong@lunaris.hanmesoft.co.kr>)
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* add some test cases to the EUC_JP regression test
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* fix problem in regress/regress.sh in case of System V
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* fix toupper(), tolower() to handle 8bit chars
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Mar 25, 1998 MB PL2 is incorporated into PostgreSQL 6.3.1
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Mar 10, 1998 PL2 released
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* add regression test for EUC_JP, EUC_CN and MULE_INTERNAL
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* add an English document (this file)
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* fix problems concerning 8-bit single byte characters
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Mar 1, 1998 PL1 released
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