PostgreSQL 按拼音排序 - convert to GBK/EUC_CN coding
背景
国内的应用，在文本排序上基本都是按照拼音来进行排序的。
在不同的字符集中，汉字的编码可能不一样，比如UTF8和GBK，其中GBK是按拼音的顺序进行编码的，而UTF8则不是。
所以如果你的数据库使用了UTF8编码，对中文字段进行排序时，可能得到的并不是按拼音排序的结果。
在PostgreSQL中，中文按拼音排序的编码包括GB18030, EUC_CN, GBK, BIG5, EUC_TW 等。
为了得到拼音排序，可以使用编码转换后的值来排序，索引也可以使用编码转换的表达式索引。
编码
PostgreSQL支持的编码如下
https://www.postgresql.org/docs/9.6/static/multibyte.html
PostgreSQL Character Sets
| 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 |
与中文编码排序相关的包括 GB18030, EUC_CN, GBK, BIG5, EUC_TW
简体常用的包括GBK, EUC_CN。
编码转换
在PostgreSQL中，如果要将字符从一个编码转换为另一个编码，需要告诉数据库（create conversion）怎么转换（使用什么C函数），PG内置了一些转换的C函数和转换方法。
https://www.postgresql.org/docs/9.6/static/catalog-pg-conversion.html
pg_conversion
| Name | Type | References | Description |
|---|---|---|---|
| oid | oid | - | Row identifier (hidden attribute; must be explicitly selected) |
| conname | name | - | Conversion name (unique within a namespace) |
| connamespace | oid | pg_namespace.oid | The OID of the namespace that contains this conversion |
| conowner | oid | pg_authid.oid | Owner of the conversion |
| conforencoding | int4 | - | Source encoding ID |
| contoencoding | int4 | - | Destination encoding ID |
| conproc | regproc | pg_proc.oid | Conversion procedure |
| condefault | bool | - | True if this is the default conversion |
查看内置的转换方法
可以看到utf8转换为中文编码的都支持了
postgres=> select * from pg_conversion where conname ~* 'gbk|gb18|euc_cn|euc_tw|big5' order by 1;
conname | connamespace | conowner | conforencoding | contoencoding | conproc | condefault
-----------------+--------------+----------+----------------+---------------+-----------------+------------
big5_to_euc_tw | 11 | 10 | 36 | 4 | big5_to_euc_tw | t
big5_to_mic | 11 | 10 | 36 | 7 | big5_to_mic | t
big5_to_utf8 | 11 | 10 | 36 | 6 | big5_to_utf8 | t
euc_cn_to_mic | 11 | 10 | 2 | 7 | euc_cn_to_mic | t
euc_cn_to_utf8 | 11 | 10 | 2 | 6 | euc_cn_to_utf8 | t
euc_tw_to_big5 | 11 | 10 | 4 | 36 | euc_tw_to_big5 | t
euc_tw_to_mic | 11 | 10 | 4 | 7 | euc_tw_to_mic | t
euc_tw_to_utf8 | 11 | 10 | 4 | 6 | euc_tw_to_utf8 | t
gb18030_to_utf8 | 11 | 10 | 39 | 6 | gb18030_to_utf8 | t
gbk_to_utf8 | 11 | 10 | 37 | 6 | gbk_to_utf8 | t
mic_to_big5 | 11 | 10 | 7 | 36 | mic_to_big5 | t
mic_to_euc_cn | 11 | 10 | 7 | 2 | mic_to_euc_cn | t
mic_to_euc_tw | 11 | 10 | 7 | 4 | mic_to_euc_tw | t
utf8_to_big5 | 11 | 10 | 6 | 36 | utf8_to_big5 | t
utf8_to_euc_cn | 11 | 10 | 6 | 2 | utf8_to_euc_cn | t
utf8_to_euc_tw | 11 | 10 | 6 | 4 | utf8_to_euc_tw | t
utf8_to_gb18030 | 11 | 10 | 6 | 39 | utf8_to_gb18030 | t
utf8_to_gbk | 11 | 10 | 6 | 37 | utf8_to_gbk | t
(18 rows)
编码转换函数
注意数据库版本
PostgreSQL 8.x(如Greenplum), 将字符串从原编码转换为指定编码的字符串返回。
可能存在显示的问题。
List of functions
Schema | Name | Result data type | Argument data types | Type
------------+---------------+------------------+---------------------+--------
pg_catalog | convert | text | text, name | normal
pg_catalog | convert | text | text, name, name | normal
PostgreSQL 9.x, 将源编码字符串的字节流转换为指定编码的字符串的字节流返回。
避免了显示的问题。
List of functions
Schema | Name | Result data type | Argument data types | Type
------------+--------------+------------------+---------------------+--------
pg_catalog | convert | bytea | bytea, name, name | normal
pg_catalog | convert_from | text | bytea, name | normal
pg_catalog | convert_to | bytea | text, name | normal
如果8.x需要避免显示问题，返回字节流，可以这样使用，推荐使用。
byteain(textout(convert(字符,'源编码','目标编码')))
例子
当前数据库编码为UTF-8，中文排序未按拼音排序。
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+---------+-------+-----------------------
db0 | postgres | UTF8 | C | C |
postgres | postgres | UTF8 | C | C |
template0 | postgres | UTF8 | C | C | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | C | C | =c/postgres +
| | | | | postgres=CTc/postgres
(4 rows)
postgres=# select * from (values ('刘德华'), ('刘少奇')) t(id) order by id;
id
--------
刘少奇
刘德华
(2 rows)
按拼音排序方法(目标可以改成EUC_CN)
8.x
postgres=> select * from (values ('刘德华'), ('刘少奇')) t(id) order by byteain(textout(convert(id,'UTF-8','GBK')));
id
--------
刘德华
刘少奇
(2 rows)
9.x
postgres=# select * from (values ('刘德华'), ('刘少奇')) t(id) order by convert(id::bytea,'UTF-8','GBK');
id
--------
刘德华
刘少奇
(2 rows)
注意多音字
中文有一些多音字，比如重庆(chongqing), 但是编码时它可能是按zhong编码的，所以看这个例子。
postgres=> select * from (values ('中山'), ('重庆')) t(id) order by byteain(textout(convert(id,'UTF-8','GBK')));
id
------
中山
重庆
(2 rows)
索引
表达式索引即可，使用immutable function.
代码
8.x
postgres=> \df+ convert
List of functions
Schema | Name | Result data type | Argument data types | Type | Data access | Volatility | Owner | Language | Source code | Description
------------+---------+------------------+---------------------+--------+-------------+------------+-----------+----------+-------------+---------------------------------------------------------
pg_catalog | convert | text | text, name | normal | no sql | stable | xxx | internal | pg_convert | convert string with specified destination encoding name
pg_catalog | convert | text | text, name, name | normal | no sql | stable | xxx | internal | pg_convert2 | convert string with specified encoding names
(2 rows)
9.x
postgres=# \df+ convert
List of functions
Schema | Name | Result data type | Argument data types | Type | Volatility | Parallel | Owner | Security | Access privileges | Language | Source code | Description
------------+---------+------------------+---------------------+--------+------------+----------+----------+----------+-------------------+----------+-------------+----------------------------------------------
pg_catalog | convert | bytea | bytea, name, name | normal | stable | safe | postgres | invoker | | internal | pg_convert | convert string with specified encoding names
(1 row)
src/backend/utils/mb/mbutils.c
/*
* Convert string between two arbitrary encodings.
*
* BYTEA convert(BYTEA string, NAME src_encoding_name, NAME dest_encoding_name)
*/
Datum
pg_convert(PG_FUNCTION_ARGS)
{
bytea *string = PG_GETARG_BYTEA_PP(0);
char *src_encoding_name = NameStr(*PG_GETARG_NAME(1));
int src_encoding = pg_char_to_encoding(src_encoding_name);
char *dest_encoding_name = NameStr(*PG_GETARG_NAME(2));
int dest_encoding = pg_char_to_encoding(dest_encoding_name);
const char *src_str;
char *dest_str;
bytea *retval;
int len;
if (src_encoding < 0)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid source encoding name \"%s\"",
src_encoding_name)));
if (dest_encoding < 0)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid destination encoding name \"%s\"",
dest_encoding_name)));
/* make sure that source string is valid */
len = VARSIZE_ANY_EXHDR(string);
src_str = VARDATA_ANY(string);
pg_verify_mbstr_len(src_encoding, src_str, len, false);
/* perform conversion */
dest_str = (char *) pg_do_encoding_conversion((unsigned char *) src_str,
len,
src_encoding,
dest_encoding);
/* update len if conversion actually happened */
if (dest_str != src_str)
len = strlen(dest_str);
/*
* build bytea data type structure.
*/
retval = (bytea *) palloc(len + VARHDRSZ);
SET_VARSIZE(retval, len + VARHDRSZ);
memcpy(VARDATA(retval), dest_str, len);
if (dest_str != src_str)
pfree(dest_str);
/* free memory if allocated by the toaster */
PG_FREE_IF_COPY(string, 0);
PG_RETURN_BYTEA_P(retval);
}
使用字段或排序collate语法纠正排序顺序
使用binary存储格式排序，只能通过编码来修正排序顺序。
除此之外，我们还可以在不改编码的情况下，使用字段或者order by的collate语法来修正排序顺序。
例子
select * from pg_collation ;
设置列级collate
create table a (c1 text collate "zh_CN.utf8");
修改列collate,会导致rewrite table
alter table a alter c1 type text COLLATE "zh_CN.utf8";
设置排序级collate
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.utf8";
c1
--------
刘德华
刘少奇
(2 rows)
设置operator collate
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.utf8";
c1
----
(0 rows)
设置库级collate
postgres=# create database test with template template0 encoding 'UTF8' lc_collate 'zh_CN.utf8';
postgres=# \c test
You are now connected to database "test" as user "postgres".
test=# create table a (c1 text);
CREATE TABLE
test=# insert into a values ('刘德华'),('刘少奇');
INSERT 0 2
test=# select * from a order by c1;
c1
--------
刘德华
刘少奇
(2 rows)
注意索引和创建索引时的collate必须一致，才能使用该索引
postgres=# create table a(c1 text);
CREATE TABLE
postgres=# create index idxa on a(c1 collate "zh_CN.utf8");
CREATE INDEX
postgres=# explain select * from a order by c1;
QUERY PLAN
----------------------------------------------------------------
Sort (cost=10000000094.38..10000000097.78 rows=1360 width=32)
Sort Key: c1
-> Seq Scan on a (cost=0.00..23.60 rows=1360 width=32)
(3 rows)
postgres=# explain select * from a order by c1 collate "zh_CN.utf8";
QUERY PLAN
------------------------------------------------------------------------
Index Only Scan using idxa on a (cost=0.15..31.55 rows=1360 width=64)
(1 row)
参考
1. https://www.postgresql.org/docs/9.6/static/multibyte.html#AEN39011
2. https://www.postgresql.org/docs/9.6/static/sql-createconversion.html
3. https://www.postgresql.org/docs/9.6/static/catalog-pg-conversion.html