标签
PostgreSQL , create database , collate , ctype , pg_encoding , pg_encoding_to_char()
背景
PostgreSQL实例支持创建多个数据库，创建数据库时，可以指定模板库，并为每个数据库设置不同的字符集、本地化collate, 货币等属性。
接下来举例讲述CREATE DATABASE的具体使用方法。
一、CREATE DATABASE语法
Command: CREATE DATABASE
Description: create a new database
Syntax:
CREATE DATABASE name
[ [ WITH ] [ OWNER [=] user_name ]
[ TEMPLATE [=] template ]
[ ENCODING [=] encoding ]
[ LC_COLLATE [=] lc_collate ]
[ LC_CTYPE [=] lc_ctype ]
[ TABLESPACE [=] tablespace_name ]
[ CONNECTION LIMIT [=] connlimit ] ]
二、克隆模板库(从指定模板创建数据库)
例子
以test数据库为模板，克隆一个名为test01的数据库。
test=> create database test01 with template test;
CREATE DATABASE
如果不指定模板，则默认的模板为template1。
注意
从指定模板库创建数据库，除了当前连接，不能有其他用户连在对应的模板库上面。
如果有其他用户连在test库，可能会报类似这样的错误
test=> create database test01 with template test;
ERROR: source database "test" is being accessed by other users
DETAIL: There is 1 other session using the database.
三、创建数据库时，如何指定encoding
PostgreSQL支持哪些encoding
用户可以参考PostgreSQL的官方文档，有对应的字符集支持列表
https://www.postgresql.org/docs/9.6/static/multibyte.html
Server=Yes表示该字符集支持用于create database。否则只支持作为客户端字符集。
| Name | Description | Language | Server? | Bytes/Char | Aliases |
|---|---|---|---|---|---|
| BIG5 | Big Five | Traditional Chinese | No | 1-2 | WIN950, Windows950 |
| EUC_CN | Extended UNIX Code-CN | Simplified Chinese | Yes | 1-3 | - |
| EUC_JP | Extended UNIX Code-JP | Japanese | Yes | 1-3 | - |
| EUC_JIS_2004 | Extended UNIX Code-JP, JIS X 0213 | Japanese | Yes | 1-3 | - |
| EUC_KR | Extended UNIX Code-KR | Korean | Yes | 1-3 | - |
| EUC_TW | Extended UNIX Code-TW | Traditional Chinese, Taiwanese | Yes | 1-3 | - |
| GB18030 | National Standard | Chinese | No | 1-4 | - |
| GBK | Extended National Standard | Simplified Chinese | No | 1-2 | WIN936, Windows936 |
| ISO_8859_5 | ISO 8859-5, ECMA 113 | Latin/Cyrillic | Yes | 1 | - |
| ISO_8859_6 | ISO 8859-6, ECMA 114 | Latin/Arabic | Yes | 1 | - |
| ISO_8859_7 | ISO 8859-7, ECMA 118 | Latin/Greek | Yes | 1 | - |
| ISO_8859_8 | ISO 8859-8, ECMA 121 | Latin/Hebrew | Yes | 1 | - |
| JOHAB | JOHAB | Korean (Hangul) | No | 1-3 | - |
| KOI8R | KOI8-R | Cyrillic (Russian) | Yes | 1 | KOI8 |
| KOI8U | KOI8-U | Cyrillic (Ukrainian) | Yes | 1 | - |
| LATIN1 | ISO 8859-1, ECMA 94 | Western European | Yes | 1 | ISO88591 |
| LATIN2 | ISO 8859-2, ECMA 94 | Central European | Yes | 1 | ISO88592 |
| LATIN3 | ISO 8859-3, ECMA 94 | South European | Yes | 1 | ISO88593 |
| LATIN4 | ISO 8859-4, ECMA 94 | North European | Yes | 1 | ISO88594 |
| LATIN5 | ISO 8859-9, ECMA 128 | Turkish | Yes | 1 | ISO88599 |
| LATIN6 | ISO 8859-10, ECMA 144 | Nordic | Yes | 1 | ISO885910 |
| LATIN7 | ISO 8859-13 | Baltic | Yes | 1 | ISO885913 |
| LATIN8 | ISO 8859-14 | Celtic | Yes | 1 | ISO885914 |
| LATIN9 | ISO 8859-15 | LATIN1 with Euro and accents | Yes | 1 | ISO885915 |
| LATIN10 | ISO 8859-16, ASRO SR 14111 | Romanian | Yes | 1 | ISO885916 |
| MULE_INTERNAL | Mule internal code | Multilingual Emacs | Yes | 1-4 | - |
| SJIS | Shift JIS | Japanese | No | 1-2 | Mskanji, ShiftJIS, WIN932, Windows932 |
| SHIFT_JIS_2004 | Shift JIS, JIS X 0213 | Japanese | No | 1-2 | - |
| SQL_ASCII | unspecified (see text) | any | Yes | 1 | - |
| UHC | Unified Hangul Code | Korean | No | 1-2 | WIN949, Windows949 |
| UTF8 | Unicode, 8-bit | all | Yes | 1-4 | Unicode |
| WIN866 | Windows CP866 | Cyrillic | Yes | 1 | ALT |
| WIN874 | Windows CP874 | Thai | Yes | 1 | - |
| WIN1250 | Windows CP1250 | Central European | Yes | 1 | - |
| WIN1251 | Windows CP1251 | Cyrillic | Yes | 1 | WIN |
| WIN1252 | Windows CP1252 | Western European | Yes | 1 | - |
| WIN1253 | Windows CP1253 | Greek | Yes | 1 | - |
| WIN1254 | Windows CP1254 | Turkish | Yes | 1 | - |
| WIN1255 | Windows CP1255 | Hebrew | Yes | 1 | - |
| WIN1256 | Windows CP1256 | Arabic | Yes | 1 | - |
| WIN1257 | Windows CP1257 | Baltic | Yes | 1 | - |
| WIN1258 | Windows CP1258 | Vietnamese | Yes | 1 | ABC, TCVN, TCVN5712, VSCII |
创建指定encoding的数据库
例子
创建一个UTF-8字符集的数据库
test=> create database test02 with encoding 'UTF-8';
CREATE DATABASE
注意
1. 指定的字符集必须是模板库字符集的超集，否则会报错。
2. 指定的lc_ctype和lc_collate必须与目标字符集兼容。
例子，template1是默认模板库，它的字符集为UTF8。
test=> \l template1
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
template1 | xxxxxxxx | UTF8 | zh_CN.UTF-8 | zh_CN.UTF-8 | =c/xxxxxxxx +
| | | | | xxxxxxxx=CTc/xxxxxxxx
(1 row)
创建一个EUC_CN字符集的数据库
报错1，EUC_CN字符集与模板库的lc_collate,lc_ctype不兼容。
test=> create database test03 with encoding 'EUC_CN';
ERROR: encoding "EUC_CN" does not match locale "zh_CN.UTF-8"
DETAIL: The chosen LC_CTYPE setting requires encoding "UTF8".
报错2，EUC_CN字符集与模板库的字符集UTF-8不兼容。
test=> create database test03 with encoding 'EUC_CN' lc_collate='C' lc_ctype='C';
ERROR: new encoding (EUC_CN) is incompatible with the encoding of the template database (UTF8)
HINT: Use the same encoding as in the template database, or use template0 as template.
四、如何获取字符集支持的LC_COLLATE, LC_CTYPE信息
使用如下SQL可以查询系统表pg_collation得到字符集支持的lc_collate和lc_ctype。
其中encoding为空时，表示这个collation支持所有的字符集。
test=> select pg_encoding_to_char(collencoding) as encoding,collname,collcollate,collctype from pg_collation ;
encoding | collname | collcollate | collctype
------------+-----------------------+-----------------------+-----------------------
| default | |
| C | C | C
| POSIX | POSIX | POSIX
UTF8 | aa_DJ | aa_DJ.utf8 | aa_DJ.utf8
LATIN1 | aa_DJ | aa_DJ | aa_DJ
LATIN1 | aa_DJ.iso88591 | aa_DJ.iso88591 | aa_DJ.iso88591
UTF8 | aa_DJ.utf8 | aa_DJ.utf8 | aa_DJ.utf8
UTF8 | aa_ER | aa_ER | aa_ER
UTF8 | aa_ER.utf8 | aa_ER.utf8 | aa_ER.utf8
.......
EUC_CN | zh_CN | zh_CN | zh_CN
UTF8 | zh_CN | zh_CN.utf8 | zh_CN.utf8
EUC_CN | zh_CN.gb2312 | zh_CN.gb2312 | zh_CN.gb2312
UTF8 | zh_CN.utf8 | zh_CN.utf8 | zh_CN.utf8
UTF8 | zh_HK | zh_HK.utf8 | zh_HK.utf8
UTF8 | zh_HK.utf8 | zh_HK.utf8 | zh_HK.utf8
EUC_CN | zh_SG | zh_SG | zh_SG
UTF8 | zh_SG | zh_SG.utf8 | zh_SG.utf8
EUC_CN | zh_SG.gb2312 | zh_SG.gb2312 | zh_SG.gb2312
UTF8 | zh_SG.utf8 | zh_SG.utf8 | zh_SG.utf8
EUC_TW | zh_TW | zh_TW.euctw | zh_TW.euctw
UTF8 | zh_TW | zh_TW.utf8 | zh_TW.utf8
EUC_TW | zh_TW.euctw | zh_TW.euctw | zh_TW.euctw
UTF8 | zh_TW.utf8 | zh_TW.utf8 | zh_TW.utf8
UTF8 | zu_ZA | zu_ZA.utf8 | zu_ZA.utf8
LATIN1 | zu_ZA | zu_ZA | zu_ZA
LATIN1 | zu_ZA.iso88591 | zu_ZA.iso88591 | zu_ZA.iso88591
UTF8 | zu_ZA.utf8 | zu_ZA.utf8 | zu_ZA.utf8
(869 rows)
五、创建数据库时指定LC_COLLATE, LC_CTYPE
例子
创建一个数据库，lc_collate, lc_ctype分别为zh_CN.utf8
test=> create database test05 with encoding 'UTF-8' template template0 lc_collate='zh_CN.utf8' lc_ctype='zh_CN.utf8';
CREATE DATABASE
注意
如果指定的lc_collate, lc_ctype与模板库的collate,ctype不兼容，会报错。
test=> create database test04 with encoding 'UTF-8' lc_collate='zh_CN.utf8' lc_ctype='zh_CN.utf8';
ERROR: new collation (zh_CN.utf8) is incompatible with the collation of the template database (zh_CN.UTF-8)
HINT: Use the same collation as in the template database, or use template0 as template.
解决办法1，使用兼容的collate和ctype。
test=> create database test04 with encoding 'UTF-8' lc_collate='zh_CN.UTF-8' lc_ctype='zh_CN.UTF-8';
CREATE DATABASE
解决办法2，使用template0作为模板库。
test=> create database test05 with encoding 'UTF-8' template template0 lc_collate='zh_CN.utf8' lc_ctype='zh_CN.utf8';
CREATE DATABASE
六、如何修改已有数据库的collate,ctype
目前无法直接通过alter database的语法进行修改，用户可以使用创建新的数据库，导出，再导入的方式。
例子
1. 创建新数据库，指定目标collate和ctype
2. 使用pg_dump或其他客户端工具逻辑导出源数据库的数据
3. 使用pg_restore或其他客户端工具，将第二步导出数据导入新数据库
参考
https://www.postgresql.org/docs/9.6/static/sql-createdatabase.html
