前言:

字符集就是一套文字符号及其编码比较规则的集合。MySQL数据库字符集包括字符集（CHARACTER）和校对规则(COLLATION)两个概念。其中，字符集用来定义MySQL数据字符串的存储方式。而校对规则是定义比较字符串的方式。不乱码的总体原则是部署的java程序，Linux系统，MySQL客户端，MySQL服务端，

MySQL的某个库，MySQL的某个库下表的字符集统一。

1>java程序中设置：页面中:contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"

request.setCharacterEncoding("utf-8");

2>linux系统查看字符集:

A>查看Linux系统字符集(Centos7)

[root@lll2 /]# cat /etc/locale.conf

LANG="zh_CN.UTF-8"

B>修改Linux系统字符集

[root@lll2 /]# vim /etc/locale.conf

3>MySQL客户端(默认情况下 character_set_client，character_set_connection，character_set_results 会根据你Linux系统设置的字符集，而设置成什么字符集):

A>查看MySQL客户端字符集

mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name            | Value                                     |
+--------------------------+-------------------------------------------+
| character_set_client     | utf8                                      |
| character_set_connection | utf8                                      |
| character_set_database   | utf8                                      |
| character_set_filesystem | binary                                    |
| character_set_results    | utf8                                      |
| character_set_server     | utf8                                      |
| character_set_system     | utf8                                      |
| character_sets_dir       | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+
8 rows in set (0.03 sec)

B>修改MySQL客户端字符集

[client]
#password= your_password
port= 3306
socket= /tmp/mysqld.sock

default-character-set=utf8

注意:通过/etc/my.conf下修改MySQL客户端字符集不需要重启MySQL,退出重新登录就生效。

4>MySQL服务端:

A>查看MySQL客户端字符集

mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name            | Value                                     |
+--------------------------+-------------------------------------------+
| character_set_client     | utf8                                      |
| character_set_connection | utf8                                      |
| character_set_database   | utf8                                      |
| character_set_filesystem | binary                                    |
| character_set_results    | utf8                                      |
| character_set_server     | utf8                                      |
| character_set_system     | utf8                                      |
| character_sets_dir       | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+

B>修改MySQL服务器端字符集

[mysqld]
port= 3306
socket= /tmp/mysqld.sock
character_set_server=utf8
skip-external-locking
#character_set_server=utf-8    适用于5.5
#default_character_set=utf-8 适用于5.1及以下

总结：A.通过/etc/my.conf下修改MySQL服务端字符集都需要重启MySQL来生效。

B.在/etc/my.conf下修改MySQL服务端字符集会修改character_set_server,character_set_database两个参数。

5>MySQL的某个库( 如果建库时没有指定字符集，则该库会默认使用character_set_server的字符集)

A>查看创建库的字符集

mysql> show create database mysql\G;
*************************** 1. row ***************************Database: mysql
Create Database: CREATE DATABASE `mysql` /*!40100 DEFAULT CHARACTER SET utf8 */
1 row in set (0.06 sec)
B>修改库的字符集
alter database mysql character set utf8;

6>MySQL库下的表(如果建表时没有指定字符集则默认使用所属库的字符集,表中的列没有指定字符集默认都使用表的字符集)

A>查看创建表时的字符集

mysql> show create table user\G;
*************************** 1. row ***************************Table: user
Create Table: CREATE TABLE `user` (`Host` char(60) COLLATE utf8_bin NOT NULL DEFAULT '',`User` char(16) COLLATE utf8_bin NOT NULL DEFAULT '',`Password` char(41) CHARACTER SET latin1 COLLATE latin1_bin NOT NULL DEFAULT '',`Select_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Insert_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Update_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Delete_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Create_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Drop_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Reload_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Shutdown_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Process_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`File_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Grant_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`References_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Index_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Alter_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Show_db_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Super_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Create_tmp_table_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Lock_tables_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Execute_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Repl_slave_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Repl_client_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Create_view_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Show_view_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Create_routine_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Alter_routine_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Create_user_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Event_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Trigger_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`Create_tablespace_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',`ssl_type` enum('','ANY','X509','SPECIFIED') CHARACTER SET utf8 NOT NULL DEFAULT '',`ssl_cipher` blob NOT NULL,`x509_issuer` blob NOT NULL,`x509_subject` blob NOT NULL,`max_questions` int(11) unsigned NOT NULL DEFAULT '0',`max_updates` int(11) unsigned NOT NULL DEFAULT '0',`max_connections` int(11) unsigned NOT NULL DEFAULT '0',`max_user_connections` int(11) unsigned NOT NULL DEFAULT '0',`plugin` char(64) COLLATE utf8_bin DEFAULT '',`authentication_string` text COLLATE utf8_bin,PRIMARY KEY (`Host`,`User`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Users and global privileges'
1 row in set (0.06 sec)
B>修改表的字符集
alter table user convert to character set utf8;

7>set names latin1背后的原理

mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name            | Value                                     |
+--------------------------+-------------------------------------------+
| character_set_client     | utf8                                      |
| character_set_connection | utf8                                      |
| character_set_database   | utf8                                      |
| character_set_filesystem | binary                                    |
| character_set_results    | utf8                                      |
| character_set_server     | utf8                                      |
| character_set_system     | utf8                                      |
| character_sets_dir       | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+
8 rows in set (0.01 sec)
mysql> set names latin1;
Query OK, 0 rows affected (0.01 sec)
mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name            | Value                                     |
+--------------------------+-------------------------------------------+
| character_set_client     | latin1                                    |
| character_set_connection | latin1                                    |
| character_set_database   | utf8                                      |
| character_set_filesystem | binary                                    |
| character_set_results    | latin1                                    |
| character_set_server     | utf8                                      |
| character_set_system     | utf8                                      |
| character_sets_dir       | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+
8 rows in set (0.00 sec)

总结:

set names latin1就是把上面三个参数改成了latin1。也就是说character_set_client,character_set_connection,character_set_results三者的字符集默认会和

linux系统的字符集一致，但是当在mysql中执行set names字符集操作后,这三者都会改为设置的字符集,但是命令修改时临时生效的。

root@lll2 /]# mysql -u root -p --default-character-set=latin1带字符集登录原理也是临时修改那三个参数。