转贴自http://www.itpub.net/thread-662823-1-1.html
参考来源:http://www.banping.com/2011/01/24/mysql-character-collation/
提示: 普通用户下的更改,而非root用户下的字符集更改的差别(root用户下更改的相关参数不变)
MySQL 服务端不加任何参数启动时，客户端可以默认正常显示汉字，如下面所示
PHP code:
D:mysql5>.binmysqld-max-nt.exe --console
061106 20:35:21 InnoDB: Started; log sequence number 0 43655
061106 20:35:22 [Note] .binmysqld-max-nt.exe: ready for connections.
Version: '5.0.18-nt-max' socket: '' port: 3306 MySQL Community Edition (GPL)
Microsoft Windows XP [版本 5.1.2600]
(C) 版权所有 1985-2001 Microsoft Corp.
C:Documents and SettingsAdministrator>cd d:mysql5bin
C:Documents and SettingsAdministrator>d:
D:mysql5bin>mysql -uroot
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 1 to server version: 5.0.18-nt-max
Type 'help;' or 'h' for help. Type 'c' to clear the buffer.
mysql> use test
Database changed
mysql> SHOW VARIABLES LIKE 'character_set%';
+--------------------------+---------------------------+
| Variable_name | Value |
+--------------------------+---------------------------+
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | latin1 |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | D:mysql5sharecharsets |
+--------------------------+---------------------------+
7 rows in set (0.00 sec)
mysql> create table ad(name varchar(32));
Query OK, 0 rows affected (0.10 sec)
mysql> insert into ad values('汉字');
Query OK, 1 row affected (0.00 sec)
mysql> select * from ad;
+------+
| name |
+------+
| 汉字 |
+------+
1 row in set (0.00 sec)
mysql>
此时，插入、显示字段的汉字值都正确。
但是如果服务器启动的时候指定了字符集参数，或者配置文件里面包含字符集参数
情况就不同了
my.ini
[mysqld]
default-character-set=gbk
D:mysql5>.binmysqld-max-nt.exe --defaults-file=my.ini --ansi --console
InnoDB: Error: log file .ib_logfile0 is of different size 0 5242880 bytes
InnoDB: than specified in the .cnf file 0 8388608 bytes!
061106 21:31:06 [Note] .binmysqld-max-nt.exe: ready for connections.
Version: '5.0.18-nt-max' socket: '' port: 3306 MySQL Community Edition (GPL)
061106 21:37:46 [Note] .binmysqld-max-nt.exe: Normal shutdown
061106 21:37:48 [Note] .binmysqld-max-nt.exe: Shutdown complete
D:mysql5>binmysqld-max-nt.exe --character_set_server=gbk --console
InnoDB: Error: log file .ib_logfile0 is of different size 0 5242880 bytes
InnoDB: than specified in the .cnf file 0 8388608 bytes!
061106 21:39:55 [Note] binmysqld-max-nt.exe: ready for connections.
Version: '5.0.18-nt-max' socket: '' port: 3306 MySQL Community Edition (GPL)
此时，显示过去未指定字符集时建立的表并插入汉字的字段，显示是正常的
D:mysql5bin>mysql -uroot
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 1 to server version: 5.0.18-nt-max
Type 'help;' or 'h' for help. Type 'c' to clear the buffer.
mysql> use test
Database changed
mysql> select * from ad;
+------+
| name |
+------+
| 汉字 |
+------+
1 row in set (0.00 sec)
mysql> SHOW VARIABLES LIKE 'character_set%';
+--------------------------+---------------------------+
| Variable_name | Value |
+--------------------------+---------------------------+
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | gbk |
| character_set_results | latin1 |
| character_set_server | gbk |
| character_set_system | utf8 |
| character_sets_dir | D:mysql5sharecharsets |
+--------------------------+---------------------------+
7 rows in set (0.00 sec)
这个时候建立的表并插入汉字的字段，不能正确显示
mysql> create table ad2(name varchar(32));
Query OK, 0 rows affected (0.06 sec)
mysql> insert into ad2 values('汉字');
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> select * from ad2;
+------+
| name |
+------+
| ??? |
+------+
1 row in set (0.01 sec)
如果只在客户端设定character_set_results参数，那么不管服务器端是什么字符集时建立、插入汉字的表都显示不正确
mysql> set character_set_results='gbk';
Query OK, 0 rows affected (0.00 sec)
mysql> SHOW VARIABLES LIKE 'character_set%';
+--------------------------+---------------------------+
| Variable_name | Value |
+--------------------------+---------------------------+
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | gbk |
| character_set_results | gbk |
| character_set_server | gbk |
| character_set_system | utf8 |
| character_sets_dir | D:mysql5sharecharsets |
+--------------------------+---------------------------+
7 rows in set (0.00 sec)
mysql> select * from ad2;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
mysql> select * from ad;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
如果再设定character_set_client，效果和只设定character_set_results没有什么差别
mysql> set character_set_client='gbk';
Query OK, 0 rows affected (0.00 sec)
mysql> select * from ad;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
mysql> select * from ad2;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
mysql> create table ad3(name varchar(32));
Query OK, 0 rows affected (0.05 sec)
mysql> insert into ad3 values('汉字');
Query OK, 1 row affected (0.00 sec)
mysql> select * from ad3;
+------+
| name |
+------+
| ?? |
+------+
1 row in set (0.01 sec)
mysql> SHOW VARIABLES LIKE 'character_set%';
+--------------------------+---------------------------+
| Variable_name | Value |
+--------------------------+---------------------------+
| character_set_client | gbk |
| character_set_connection | latin1 |
| character_set_database | gbk |
| character_set_results | gbk |
| character_set_server | gbk |
| character_set_system | utf8 |
| character_sets_dir | D:mysql5sharecharsets |
+--------------------------+---------------------------+
7 rows in set (0.00 sec)
如果再设定character_set_connection，不影响已经建立和插入的表，但是新建立、插入汉字的表就能正确显示
mysql> set character_set_connection='gbk';
Query OK, 0 rows affected (0.00 sec)
mysql> select * from ad3;
+------+
| name |
+------+
| ?? |
+------+
1 row in set (0.00 sec)
mysql> select * from ad2;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
mysql> select * from ad;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
我们可以查看各个表的字符集
mysql> show create table ad;
+-------+----------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------+
| ad | CREATE TABLE `ad` (
`name` varchar(32) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1 |
+-------+----------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table ad2;
+-------+--------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------+
| ad2 | CREATE TABLE `ad2` (
`name` varchar(32) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=gbk |
+-------+--------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table ad3;
+-------+--------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------+
| ad3 | CREATE TABLE `ad3` (
`name` varchar(32) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=gbk |
+-------+--------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
此时新建的表、此时插入汉字，显示就正确了
mysql> set character_set_client=gbk;
Query OK, 0 rows affected (0.00 sec)
mysql> set character_set_connection=gbk;
Query OK, 0 rows affected (0.00 sec)
mysql> set character_set_results=gbk;
Query OK, 0 rows affected (0.00 sec)
mysql> create table ad4(name varchar(32));
Query OK, 0 rows affected (0.06 sec)
mysql> insert into ad4 values('汉字');
Query OK, 1 row affected (0.00 sec)
mysql> select * from ad;
+-------+
| name |
+-------+
| ??×? |
+-------+
1 row in set (0.00 sec)
mysql> select * from ad4;
+------+
| name |
+------+
| 汉字 |
+------+
1 row in set (0.00 sec)
mysql> create table ad5(name varchar(32)) DEFAULT CHARSET=gbk;
Query OK, 0 rows affected (0.10 sec)
mysql> insert into ad5 values('汉字');
Query OK, 1 row affected (0.00 sec)
mysql> select * from ad5;
+------+
| name |
+------+
| 汉字 |
+------+
1 row in set (0.00 sec)
mysql> select * from ad4;
+------+
| name |
+------+
| 汉字 |
+------+
1 row in set (0.00 sec)
mysql> show create table ad4;
+-------+--------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------+
| ad4 | CREATE TABLE `ad4` (
`name` varchar(32) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=gbk |
+-------+--------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table ad5;
+-------+--------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------+
| ad5 | CREATE TABLE `ad5` (
`name` varchar(32) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=gbk |
+-------+--------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table ad3;
+-------+--------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------+
| ad3 | CREATE TABLE `ad3` (
`name` varchar(32) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=gbk |
+-------+--------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> exit
Bye
--------------
由此，我们可以认识到，当服务器端指定字符集时。如果客户端没有指定character_set_results字符集，
那么可以正确显示服务器端未指定字符集时建立、插入汉字的表。
如果要新建的表（默认字符集已经改变为服务器端指定字符集）正确显示汉字，必须同时设定character_set_client和character_set_connection参数和
服务器端指定字符集保持一致，才能正确插入、显示。
如果只是要显示以前带字符集正确插入汉字的表，可以只在客户端指定character_set_results就够了。
实际上服务器端和客户端都未指定字符集就是所有字符集都默认latin1，也是保持一致的。
所以，如果要指定字符集，要在数据库还不包含表的时候进行比较保险。如果中途改变，可能引起数据丢失。