字符集

1.什么是字符集

#字符集：是一个系统支持的所有抽象字符的集合。字符是各种文字和符号的总称，包括各国家文字、标点符号、图形符号、数字等。

最早的字符集：ASCII码

中国的字符集：gbk，utf8，gbk2312
日本字符集：shift-JIS
韩国字符集：Euc-kr

万国编码：Unicode字符集

#常用的字符集：
	gbk:一个汉字占用2个字节
	utf8:一个汉字占用3个字节
	utf8mb4:一个汉字占用4个字节
	
#字符集修改要求：
	包含关系才可以修改
	
#查看字符集：
	mysql> show charset;

2.校验规则

#查看校验规则
mysql> show collation;
| latin7_general_ci        | latin7   |
| latin7_general_cs        | latin7   |
| latin7_bin               | latin7   |

#校验规则区别
1.以ci结尾：不区分大小写
2.以cs或者bin结尾：区分大小写

#大小写不同，相同字段也不能添加
mysql> alter table city add nAME varchar(10);
ERROR 1060 (42S21): Duplicate column name ‘nAME‘

3.统一字符集

#1.xshell字符集

#2.linux系统字符集
	#临时修改
	[root@db03 ~]# LANG=zh_CN.UTF-8
	#永久修改
	[root@db03 ~]# vim /etc/sysconfig/i18n		#Centos6
	[root@db03 ~]# vim /etc/locale.conf 		#Centos7
	LANG="zh_CN.UTF-8"
	
#3.数据库字符集
	1）cmake 字符集指定
	cmake . 
	-DDEFAULT_CHARSET=utf8 	-DDEFAULT_COLLATION=utf8_general_ci 	-DWITH_EXTRA_CHARSETS=all 	2）配置文件
	[root@db03 ~]# vim /etc/my.cnf
	[mysqld]
	character-set-server=utf8
	
#4.创建数据库时指定字符集
mysql> create database db7 charset utf8;
Query OK, 1 row affected (0.00 sec)

mysql> show create database db7;
+----------+--------------------------------------------------------------+
| Database | Create Database                                              |
+----------+--------------------------------------------------------------+
| db7      | CREATE DATABASE `db7` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+--------------------------------------------------------------+
1 row in set (0.00 sec)

#5.建表时根据库的字符集来建表
mysql> create table tb1(id int);

#6.指定字符集建表
mysql> create table tb3(id int) charset utf8mb4;
Query OK, 0 rows affected (0.01 sec)

mysql> show create table tb3;
+-------+------------------------------------------------------------------------------------------+
| Table | Create Table                                                                             |
+-------+------------------------------------------------------------------------------------------+
| tb3   | CREATE TABLE `tb3` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |
+-------+------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

#7.修改库的字符集
mysql> show create database db7;
+----------+--------------------------------------------------------------+
| Database | Create Database                                              |
+----------+--------------------------------------------------------------+
| db7      | CREATE DATABASE `db7` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+--------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter database db7 charset gbk;
Query OK, 1 row affected (0.00 sec)

mysql> show create database db7;
+----------+-------------------------------------------------------------+
| Database | Create Database                                             |
+----------+-------------------------------------------------------------+
| db7      | CREATE DATABASE `db7` /*!40100 DEFAULT CHARACTER SET gbk */ |
+----------+-------------------------------------------------------------+
1 row in set (0.00 sec)

#8.修改表的字符集
mysql> show create table tb2;
+-------+---------------------------------------------------------------------------------------+
| Table | Create Table                                                                          |
+-------+---------------------------------------------------------------------------------------+
| tb2   | CREATE TABLE `tb2` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter table tb2 charset gbk;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table tb2;
+-------+--------------------------------------------------------------------------------------+
| Table | Create Table                                                                         |
+-------+--------------------------------------------------------------------------------------+
| tb2   | CREATE TABLE `tb2` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=gbk |
+-------+--------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

MySQL字符集