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Add a README file for multi-byte. This file is contributed by
Chih-Chang Hsieh <cch@cc.kmu.edu.tw>, written in traditional Chinese (Big5).
This commit is contained in:
Tatsuo Ishii
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doc/README.mb.big5
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doc/README.mb.big5
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PostgreSQL 7.0.1 multi-byte (MB) support README May 20 2000
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Tatsuo Ishii
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ishii@postgresql.org
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http://www.sra.co.jp/people/t-ishii/PostgreSQL/
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[註] 1. 感謝石井達夫 (Tatsuo Ishii) 先生!
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2. 註釋部份原文所無, 中譯若有錯誤, 請聯絡 cch@cc.kmu.edu.tw
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0. 簡介
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MB 支援是為了讓 PostgreSQL 能處理多位元組字元 (multi-byte character),
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例如: EUC (Extended Unix Code), Unicode (統一碼) 和 Mule internal code
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(多國語言內碼). 在 MB 的支援下, 你可以在正規表示式 (regexp), LIKE 及
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其他一些函式中使用多位元組字元. 預設的編碼系統可取決於你安裝 PostgreSQL
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時的 initdb(1) 命令, 亦可由 createdb(1) 命令或建立資料庫的 SQL 命令決定.
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所以你可以有多個不同編碼系統的資料庫.
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MB 支援也解決了一些 8 位元單位元組字元集 (包含 ISO-8859-1) 的相關問題,
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(我並沒有說所有的相關問題都解決了, 我只是確認了迴歸測試執行成功,
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而一些法語字元在 MB 修補下可以使用. 如果你在使用 8 位元字元時發現了
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任何問題, 請通知我)
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1. 如何使用
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編譯 PostgreSQL 前, 執行 configure 時使用 multibyte 的選項
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% ./configure --enable-multibyte[=encoding_system]
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% ./configure --enable-multibyte[=編碼系統]
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其中的編碼系統可以指定為下面其中之一:
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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 Windows CP1251
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ALT Windows CP866
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例如:
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% ./configure --enable-multibyte=EUC_JP
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如果省略指定編碼系統, 那麼預設值就是 SQL_ASCII.
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2. 如何設定編碼
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initdb 命令定義 PostgresSQL 安裝後的預設編碼, 例如:
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% initdb -E EUC_JP
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將預設的編碼設定為 EUC_JP (Extended Unix Code for Japanese), 如果你喜歡
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較長的字串, 你也可以用 "--encoding" 而不用 "-E". 如果沒有使用 -E 或
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--encoding 的選項, 那麼編繹時的設定會成為預設值.
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你可以建立使用不同編碼的資料庫:
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% createdb -E EUC_KR korean
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這個命令會建立一個叫做 "korean" 的資料庫, 而其採用 EUC_KR 編碼.
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另外有一個方法, 是使用 SQL 命令, 也可以達到同樣的目的:
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CREATE DATABASE korean WITH ENCODING = 'EUC_KR';
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在 pg_database 系統規格表 (system catalog) 中有一個 "encoding" 的欄位,
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就是用來紀錄一個資料庫的編碼. 你可以用 psql -l 或進入 psql 後用 \l 的
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命令來查看資料庫採用何種編碼:
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$ psql -l
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List of databases
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Database | Owner | Encoding
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---------------+---------+---------------
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euc_cn | t-ishii | EUC_CN
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euc_jp | t-ishii | EUC_JP
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euc_kr | t-ishii | EUC_KR
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euc_tw | t-ishii | EUC_TW
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mule_internal | t-ishii | MULE_INTERNAL
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regression | t-ishii | SQL_ASCII
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template1 | t-ishii | EUC_JP
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test | t-ishii | EUC_JP
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unicode | t-ishii | UNICODE
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(9 rows)
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3. 前端與後端編碼的自動轉換
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[註: 前端泛指客戶端的程式, 可能是 psql 命令解譯器, 或採用 libpq 的 C
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程式, Perl 程式, 或者是透過 ODBC 的視窗應用程式. 而後端就是指 PostgreSQL
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資料庫的伺服程式]
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PostgreSQL 支援某些編碼在前端與後端間做自動轉換: [註: 這裡所謂的自動
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轉換是指你在前端及後端所宣告採用的編碼不同, 但只要 PostgreSQL 支援這
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兩種編碼間的轉換, 那麼它會幫你在存取前做轉換]
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encoding of backend available encoding of frontend
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--------------------------------------------------------------------
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EUC_JP EUC_JP, SJIS
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EUC_TW EUC_TW, BIG5
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LATIN2 LATIN2, WIN1250
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LATIN5 LATIN5, WIN, ALT
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MULE_INTERNAL EUC_JP, SJIS, EUC_KR, EUC_CN,
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EUC_TW, BIG5, LATIN1 to LATIN5,
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WIN, ALT, WIN1250
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在啟動自動編碼轉換之前, 你必須告訴 PostgreSQL 你要在前端採用何種編碼.
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有好幾個方法可以達到這個目的:
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o 在 psql 命令解譯器中使用 \encoding 這個命令
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\encoding 這個命令可以讓你馬上切換前端編碼, 例如, 你要將前端編碼切換為 SJIS,
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那麼請打:
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\encoding SJIS
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o 使用 libpq [註: PostgreSQL 資料庫的 C API 程式庫] 的函式
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psql 的 \encoding 命令其實只是去呼叫 PQsetClientEncoding() 這個函式來達到目的.
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int PQsetClientEncoding(PGconn *conn, const char *encoding)
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上式中 conn 這個參數代表一個對後端的連線, encoding 這個參數要放你想用的編碼,
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假如它成功地設定了編碼, 便會傳回 0 值, 失敗的話傳回 -1. 至於目前連線的編碼可
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利用以下函式查知:
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int PQclientEncoding(const PGconn *conn)
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這裡要注意的是: 這個函式傳回的是編碼的代號 (encoding id, 是個整數值),
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而不是編碼的名稱字串 (如 "EUC_JP"), 如果你要由編碼代號得知編碼名稱,
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必須呼叫:
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char *pg_encoding_to_char(int encoding_id)
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o 使用 PGCLIENTENCODING 這個環境變數
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如果前端底設定了 PGCLIENTENCODING 這一個環境變數, 那麼後端會做編碼自動轉換.
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[註] PostgreSQL 7.0.0 ~ 7.0.3 有個 bug -- 不認這個環境變數
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o 使用 SET CLIENT_ENCODING TO 這個 SQL 的命令
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要設定前端的編碼可以用以下這個 SQL 命令:
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SET CLIENT_ENCODING TO 'encoding';
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你也可以使用 SQL92 的語法 "SET NAMES" 達到同樣的目的:
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SET NAMES 'encoding';
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查詢目前的前端編碼可以用以下這個 SQL 命令:
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SHOW CLIENT_ENCODING;
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切換為原來預設的編碼, 用以下這個 SQL 命令:
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RESET CLIENT_ENCODING;
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[註] 使用 psql 命令解譯器時, 建議不要用這個方法, 請用 \encoding
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4. 關於 Unicode (統一碼)
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統一碼和其他編碼間的轉換可能要在 7.1 版後才會實現.
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5. 如果無法轉換會發生什麼事?
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假設你在後端選擇了 EUC_JP 這個編碼, 前端使用 LATIN1, (某些日文字元無法轉換成
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LATIN1) 在這個狀況下, 某個字元若不能轉成 LATIN1 字元集, 就會被轉成以下的型式:
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(十六進位值)
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6. 參考資料
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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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May 20, 2000
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* SJIS UDC (NEC selection IBM kanji) support contributed
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by Eiji Tokuya
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* Changes above will appear in 7.0.1
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Mar 22, 2000
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* Add new libpq functions PQsetClientEncoding, PQclientEncoding
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* ./configure --with-mb=EUC_JP
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now deprecated. use
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./configure --enable-multibyte=EUC_JP
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instead
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* Add SQL_ASCII regression test case
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* Add SJIS User Defined Character (UDC) support
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* All of above will appear in 7.0
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July 11, 1999
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* Add support for WIN1250 (Windows Czech) as a client encoding
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(contributed by Pavel Behal)
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* fix some compiler warnings (contributed by Tomoaki Nishiyama)
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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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Appendix:
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[Here is a good documentation explaining how to use WIN1250 on
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Windows/ODBC from Pavel Behal. Please note that Installation step 1)
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is not necceary in 6.5.1 -- Tatsuo]
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Version: 0.91 for PgSQL 6.5
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Author: Pavel Behal
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Revised by: Tatsuo Ishii
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Email: behal@opf.slu.cz
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Licence: The Same as PostgreSQL
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Sorry for my Eglish and C code, I'm not native :-)
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!!!!!!!!!!!!!!!!!!!!!!!!! NO WARRANTY !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Instalation:
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------------
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1) Change three affected files in source directories
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(I don't have time to create proper patch diffs, I don't know how)
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2) Compile with enabled locale and multibyte set to LATIN2
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3) Setup properly your instalation, do not forget to create locale
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variables in your profile (environment). Ex. (may not be exactly true):
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LC_ALL=cs_CZ.ISO8859-2
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LC_COLLATE=cs_CZ.ISO8859-2
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LC_CTYPE=cs_CZ.ISO8859-2
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LC_MONETARY=cs_CZ.ISO8859-2
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LC_NUMERIC=cs_CZ.ISO8859-2
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LC_TIME=cs_CZ.ISO8859-2
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4) You have to start the postmaster with locales set!
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5) Try it with Czech language, it have to sort
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5) Install ODBC driver for PgSQL into your M$ Windows
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6) Setup properly your data source. Include this line in your ODBC
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configuration dialog in field "Connect Settings:" :
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SET CLIENT_ENCODING = 'WIN1250';
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7) Now try it again, but in Windows with ODBC.
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Description:
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------------
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- Depends on proper system locales, tested with RH6.0 and Slackware 3.6,
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with cs_CZ.iso8859-2 loacle
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- Never try to set-up server multibyte database encoding to WIN1250,
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always use LATIN2 instead. There is not WIN1250 locale in Unix
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- WIN1250 encoding is useable only for M$W ODBC clients. The characters are
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on thy fly re-coded, to be displayed and stored back properly
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Important:
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----------
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- it reorders your sort order depending on your LC_... setting, so don't be
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confused with regression tests, they don't use locale
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- "ch" is corectly sorted only in some newer locales (Ex. RH6.0)
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- you have to insert money as '162,50' (with comma in aphostrophes!)
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- not tested properly
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Block a user