PostgreSQL Server Encoding sql_ascii attention
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- ……
群里一位兄弟问到的一个问题 :
" 我有一个postgresql,比较大,编码是sqlascii码,我想转换成有utf8 ,有方案可行吗? "
如果使用场景中未用到non-ASCII编码的字符, 那很幸运, 导出导入就可以了.
但是如果场景中使用了non-ASCII编码的字符, 那就没那么幸运了, 因为SQL_ASCII字符集不会对non-ASCII字符做合法性检验, 同时不做任何的编码转换, 客户端上来是什么值就是什么值.
例如 :
pgdev@db-172-16-3-150-> initdb -D $PGDATA -E SQL_ASCII --locale=C -U postgrespg_ctl start
-- 当前服务端编码
pgdev@db-172-16-3-150-> localeLANG=en_US.utf8LC_CTYPE="en_US.utf8"LC_NUMERIC="en_US.utf8"LC_TIME="en_US.utf8"LC_COLLATE="en_US.utf8"LC_MONETARY="en_US.utf8"LC_MESSAGES="en_US.utf8"LC_PAPER="en_US.utf8"LC_NAME="en_US.utf8"LC_ADDRESS="en_US.utf8"LC_TELEPHONE="en_US.utf8"LC_MEASUREMENT="en_US.utf8"LC_IDENTIFICATION="en_US.utf8"LC_ALL=psqlpostgres=# create role digoal login encrypted password 'digoal';CREATE ROLEpostgres=# create database digoal owner digoal;CREATE DATABASEdigoal=# \lList of databasesName | Owner | Encoding | Collate | Ctype | Access privileges-----------+----------+-----------+---------+-------+-----------------------digoal | digoal | SQL_ASCII | C | C |postgres=# \c digoal digoaldigoal=> create schema digoal;CREATE SCHEMAdigoal=> create table t(id int, info text);CREATE TABLEdigoal=> insert into t values (1, '中国');INSERT 0 1
-- 插入中文没有问题, 当前插入的汉字是UTF8编码.
digoal=> \qpgdev@db-172-16-3-150-> export LANG=zh_CN.gbkpgdev@db-172-16-3-150-> localeLANG=zh_CN.gbkLC_CTYPE="zh_CN.gbk"LC_NUMERIC="zh_CN.gbk"LC_TIME="zh_CN.gbk"LC_COLLATE="zh_CN.gbk"LC_MONETARY="zh_CN.gbk"LC_MESSAGES="zh_CN.gbk"LC_PAPER="zh_CN.gbk"LC_NAME="zh_CN.gbk"LC_ADDRESS="zh_CN.gbk"LC_TELEPHONE="zh_CN.gbk"LC_MEASUREMENT="zh_CN.gbk"LC_IDENTIFICATION="zh_CN.gbk"LC_ALL=
-- 同时修改一下secureCRT的字符集.
pgdev@db-172-16-3-150-> psql digoal digoalpsql (9.3devel)Type "help" for help.digoal=> insert into t values (2, '美国');INSERT 0 1digoal=> insert into t values (3, '德国');INSERT 0 1
-- 插入中文没有问题, 当前插入的汉字是GBK编码.
digoal=> select *,info::bytea from t;id | info | info----+--------+----------------1 | 涓浗 | \xe4b8ade59bbd2 | 美国 | \xc3c0b9fa3 | 德国 | \xb5c2b9fa
-- 由于'中国' 是以UTF8编码插入的, 美国德国是以GBK编码插入的,
-- 像这种保护混合编码的数值要导出并导入到另一个UTF8编码的数据库, GBK编码的必然会导致导入失败.
-- 后面使用BYTEA插入UTF8字符集的数据库看看就知道了.
-- 插入一些字节流, SQL_ASCII对non-ASCII也就是0-127以外的值都不做判断, 直接插入.
digoal=> insert into t values (4, E'\xe2\x82\xad');INSERT 0 1
-- 0x00为0-127范围内的值, SQL_ASCII编码的无效字节. 这个是被正常的检测出来了.
digoal=> insert into t values (4, E'\xe2\x82\x00');ERROR: invalid byte sequence for encoding "SQL_ASCII": 0x00
-- 其他字节流随便插入.
digoal=> insert into t values (4, E'\xe2\x82\x01');INSERT 0 1digoal=> insert into t values (4, E'\xe2\x82\xae');INSERT 0 1
-- 由于服务端是SQL_ASCII的, 所以虽然以下编码在UTF8中是非法的, 但是插入到SQL_ASCII的数据库还是没有问题.
digoal=> set client_encoding='UTF8';SETdigoal=> insert into t values (4, E'\xe2\x82\xae');INSERT 0 1digoal=> insert into t values (4, E'\xe2\x82\x0e');INSERT 0 1digoal=> insert into t values (4, E'\x8f');INSERT 0 1
-- 查询结果 :
digoal=> select * from t;id | info----+--------1 | 涓浗2 | 美国3 | 德国4 | 鈧4 | 鈧4 | 鈧\x014 | 鈧4 | 鈧4 | 鈧\x0E4 |4 |(11 rows)
-- 如果数据库是UTF8字符集的话 :
postgres=# \lList of databasesName | Owner | Encoding | Collate | Ctype | Access privileges-------------+----------+----------+---------+-------+-----------------------digoal | digoal | UTF8 | C | C |
-- UTF8的非法字符将不允许插入.
postgres=# insert into t values (4, E'\x8f');ERROR: invalid byte sequence for encoding "UTF8": 0x8fpostgres=# insert into t values (2, E'\xc3\xc0\xb9\xfa');ERROR: invalid byte sequence for encoding "UTF8": 0xc3 0xc0postgres=# insert into t values (2, E'\xb5\xc2\xb9\xfa');ERROR: invalid byte sequence for encoding "UTF8": 0xb5
-- 即使将客户端编码改成SQL_ASCII, 插入到数据库时也是会报错的.
postgres=# set client_encoding='SQL_ASCII';SETpostgres=# insert into t values (2, E'\xc3\xc0\xb9\xfa');ERROR: invalid byte sequence for encoding "UTF8": 0xc3 0xc0postgres=# insert into t values (2, E'\xb5\xc2\xb9\xfa');ERROR: invalid byte sequence for encoding "UTF8": 0xb5postgres=# insert into t values (2, E'\xc3\xc0\xb9\xfa');ERROR: 22021: invalid byte sequence for encoding "UTF8": 0xc3 0xc0LOCATION: report_invalid_encoding, wchar.c:2015
所以如果存在混合编码的数据插入到SQL_ASCII数据库后, 要把数据正常的导入到UTF8字符集的数据库中, 是一件非常困难的事情.
需将数据导出, 并做好相应的转码再导入到数据库中.
【小结】
1. 如果数据库中需要存储非ASCII字符, 那么不推荐数据库使用SQL_ASCII字符集.
2. 使用SQL_ASCII字符集必须了解的几种情况 :
The SQL_ASCII setting behaves considerably differently from the other settings. When the server character set is SQL_ASCII, the server interprets byte values 0-127 according to the ASCII standard, while byte values 128-255 are taken as uninterpreted characters. No encoding conversion will be done when the setting is SQL_ASCII. Thus, this setting is not so much a declaration that a specific encoding is in use, as a declaration of ignorance about the encoding. In most cases, if you are working with any non-ASCII data, it is unwise to use the SQL_ASCII setting because PostgreSQL will be unable to help you by converting or validating non-ASCII characters.PostgreSQL will allow superusers to create databases with SQL_ASCII encoding even when LC_CTYPE is not C or POSIX. As noted above, SQL_ASCII does not enforce that the data stored in the database has any particular encoding, and so this choice poses risks of locale-dependent misbehavior. Using this combination of settings is deprecated and may someday be forbidden altogether.If the client character set is defined as SQL_ASCII, encoding conversion is disabled, regardless of the server's character set. Just as for the server, use of SQL_ASCII is unwise unless you are working with all-ASCII data.
【参考】
2. http://blog.163.com/digoal@126/blog/static/163877040201211281407682/
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