如何按拼音排序 - 数据库本土化特性(collate, ctype, …)
背景
数据库为了支持国际化，通常会涉及到collate, ctype的概念。
初始化数据库集群时，可以设置如下参数，用于设置数据库的字符串排序、字符归类方法、数值\日期\时间\货币的格式等。
| LC_COLLATE | String sort order |
|---|---|
| LC_CTYPE | Character classification (What is a letter? Its upper-case equivalent?) |
| LC_MESSAGES | Language of messages |
| LC_MONETARY | Formatting of currency amounts |
| LC_NUMERIC | Formatting of numbers |
| LC_TIME | Formatting of dates and times |
用户可以利用这些特性，按本土化需求，输出对应的顺序或者格式。
按中文的拼音为顺序排序就是一个常见的需求。
PostgreSQL支持哪些字符集(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 |
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)
如何设置数据库的本土化(collate)信息
《如何设置数据库的LC_COLLATE, LC_CTYPE, ENCODING, TEMPLATE》
如何设置字段的本土化(collate)
在操作前，请了解清楚与您当前数据库字符集(encoding)兼容的collate，使用如下SQL可以得到当前数据库的encoding
postgres=# select datname,pg_encoding_to_char(encoding) as encoding from pg_database;
datname | encoding
--------------------+-----------
template1 | UTF8
template0 | UTF8
db | SQL_ASCII
db1 | EUC_CN
contrib_regression | UTF8
test01 | UTF8
test02 | UTF8
postgres | UTF8
(8 rows)
1. 在创建表时，指定兼容当前字符集的collate
CREATE TABLE test1 (
a text COLLATE "de_DE",
b text COLLATE "es_ES",
...
);
2. 修改列collate(会导致rewrite table)，大表请谨慎操作
alter table a alter c1 type text COLLATE "zh_CN";
如何在SQL用使用本土化(collate)
1. 使用本土化, 改变order by输出排序
test=# select * from a order by c1 collate "C";
c1
--------
刘少奇
刘德华
(2 rows)
test=# select * from a order by c1 collate "zh_CN";
c1
--------
刘德华
刘少奇
(2 rows)
2. 使用本土化, 改变操作符的结果
test=# select * from a where c1 > '刘少奇' collate "C";
c1
--------
刘德华
(1 row)
test=# select * from a where c1 > '刘少奇' collate "zh_CN";
c1
----
(0 rows)
如何使用本土化索引, 按拼音排序
注意排序语句中的collate与索引的collate保持一致，才能使用这个索引进行排序。
postgres=# create index idxa on a(c1 collate "zh_CN");
CREATE INDEX
postgres=# explain select * from a order by c1 collate "zh_CN";
QUERY PLAN
------------------------------------------------------------------------
Index Only Scan using idxa on a (cost=0.15..31.55 rows=1360 width=64)
(1 row)
如何按拼音排序
1. 方法1，使用本土化SQL（不修改原有数据）
test=# select * from a order by c1 collate "zh_CN";
c1
--------
刘德华
刘少奇
(2 rows)
2. 方法2，使用本土化字段（如果已有数据，则需要调整原有数据）
alter table a alter c1 type text COLLATE "zh_CN";
3. 方法3，使用本土化索引以及本土化SQL（不修改原有数据）
postgres=# create index idxa on a(c1 collate "zh_CN");
CREATE INDEX
postgres=# explain select * from a order by c1 collate "zh_CN";
QUERY PLAN
------------------------------------------------------------------------
Index Only Scan using idxa on a (cost=0.15..31.55 rows=1360 width=64)
(1 row)
4. 设置数据库的collate为zh_CN，将默认使用这个collate，按拼音排序
test02=# create database test03 encoding 'UTF8' lc_collate 'zh_CN.utf8' lc_ctype 'zh_CN.utf8' template template0;
CREATE DATABASE
test02=# \c test03
You are now connected to database "test03" as user "postgres".
test03=# select * from (values ('刘德华'),('刘少奇')) as a(c1) order by c1 ;
c1
--------
刘德华
刘少奇
(2 rows)
注意多音字
有些多音字，例如重庆(chongqing), 编码时”重”可能是按zhong编码，影响输出。
test03=# select * from (values ('中山'),('重庆')) as a(c1) order by c1 collate "zh_CN";
c1
------
中山
重庆
(2 rows)
Greenplum按拼音排序
greenplum不支持单列设置collate，按拼音排序有些许不同。
在greenplum中，可以使用字符集转换，按对应二进制排序，得到拼音排序的效果。
postgres=# select * from (values ('刘德华'), ('刘少奇')) t(id) order by byteain(textout(convert(id,'UTF8','EUC_CN')));
id
--------
刘德华
刘少奇
(2 rows)
参考
《PostgreSQL 按拼音排序 - convert to GBK/EUC_CN coding》
《如何设置数据库的LC_COLLATE, LC_CTYPE, ENCODING, TEMPLATE》
https://www.postgresql.org/docs/9.6/static/charset.html