MySQL字符集

 一、mysql字符集简介

'''
mysql字符集
    字符集是一套符合和编码，校验规则（collation）是在字符集内用于比较字符的一套规则，即字符集的排序规则。MySQL可以使用对种字符集和检验规则来组织字符。
    MySQL服务器可以支持多种字符集，在同一台服务器，同一个数据库，甚至同一个表的不同字段都可以指定使用不同的字符集
    相比oracle等其他数据库管理系统，在同一个数据库只能使用相同的字符集，MySQL明显存在更大的灵活性。
'''

二、查看字符集

1、查看当前系统字符集

方式1：show variables like 'character%';

+--------------------------+---------------------------------------------------------------+
| Variable_name            | Value                                                         |
+--------------------------+---------------------------------------------------------------+
| character_set_client     | utf8mb4                                                       |
| character_set_connection | utf8mb4                                                       |
| character_set_database   | utf8mb4                                                       |
| character_set_filesystem | binary                                                        |
| character_set_results    | utf8mb4                                                       |
| character_set_server     | utf8mb4                                                       |
| character_set_system     | utf8                                                          |
| character_sets_dir       | /usr/local/mysql-5.7.17-linux-glibc2.5-x86_64/share/charsets/ |
+--------------------------+---------------------------------------------------------------+

 方式2：show variables like 'collation%';

+----------------------+--------------------+
| Variable_name        | Value              |
+----------------------+--------------------+
| collation_connection | utf8mb4_general_ci |
| collation_database   | utf8mb4_general_ci |
| collation_server     | utf8mb4_general_ci |
+----------------------+--------------------+

2、查看mysql支持的所有字符集

show charset;

+----------+-----------------------------+---------------------+--------+
| Charset  | Description                 | Default collation   | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese    | big5_chinese_ci     |      2 |
| dec8     | DEC West European           | dec8_swedish_ci     |      1 |
| cp850    | DOS West European           | cp850_general_ci    |      1 |
| hp8      | HP West European            | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian       | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European        | latin1_swedish_ci   |      1 |
| latin2   | ISO 8859-2 Central European | latin2_general_ci   |      1 |
| swe7     | 7bit Swedish                | swe7_swedish_ci     |      1 |
| ascii    | US ASCII                    | ascii_general_ci    |      1 |
| ujis     | EUC-JP Japanese             | ujis_japanese_ci    |      3 |
| sjis     | Shift-JIS Japanese          | sjis_japanese_ci    |      2 |
| hebrew   | ISO 8859-8 Hebrew           | hebrew_general_ci   |      1 |
| tis620   | TIS620 Thai                 | tis620_thai_ci      |      1 |
| euckr    | EUC-KR Korean               | euckr_korean_ci     |      2 |
| koi8u    | KOI8-U Ukrainian            | koi8u_general_ci    |      1 |
| gb2312   | GB2312 Simplified Chinese   | gb2312_chinese_ci   |      2 |
| greek    | ISO 8859-7 Greek            | greek_general_ci    |      1 |
| cp1250   | Windows Central European    | cp1250_general_ci   |      1 |
| gbk      | GBK Simplified Chinese      | gbk_chinese_ci      |      2 |
| latin5   | ISO 8859-9 Turkish          | latin5_turkish_ci   |      1 |
| armscii8 | ARMSCII-8 Armenian          | armscii8_general_ci |      1 |
| utf8     | UTF-8 Unicode               | utf8_general_ci     |      3 |
| ucs2     | UCS-2 Unicode               | ucs2_general_ci     |      2 |
| cp866    | DOS Russian                 | cp866_general_ci    |      1 |
| keybcs2  | DOS Kamenicky Czech-Slovak  | keybcs2_general_ci  |      1 |
| macce    | Mac Central European        | macce_general_ci    |      1 |
| macroman | Mac West European           | macroman_general_ci |      1 |
| cp852    | DOS Central European        | cp852_general_ci    |      1 |
| latin7   | ISO 8859-13 Baltic          | latin7_general_ci   |      1 |
| utf8mb4  | UTF-8 Unicode               | utf8mb4_general_ci  |      4 |
| cp1251   | Windows Cyrillic            | cp1251_general_ci   |      1 |
| utf16    | UTF-16 Unicode              | utf16_general_ci    |      4 |
| utf16le  | UTF-16LE Unicode            | utf16le_general_ci  |      4 |
| cp1256   | Windows Arabic              | cp1256_general_ci   |      1 |
| cp1257   | Windows Baltic              | cp1257_general_ci   |      1 |
| utf32    | UTF-32 Unicode              | utf32_general_ci    |      4 |
| binary   | Binary pseudo charset       | binary              |      1 |
| geostd8  | GEOSTD8 Georgian            | geostd8_general_ci  |      1 |
| cp932    | SJIS for Windows Japanese   | cp932_japanese_ci   |      2 |
| eucjpms  | UJIS for Windows Japanese   | eucjpms_japanese_ci |      3 |
+----------+-----------------------------+---------------------+--------+

3、查看指定库的字符集

show create database game;

+----------+------------------------------------------------------------------+
| Database | Create Database                                                  |
+----------+------------------------------------------------------------------+
| gamee     | CREATE DATABASE `game` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+------------------------------------------------------------------+

4、查看表字符集

方式1：show table status from game like 'user_id'G;

*************************** 1. row ***************************
           Name: userid
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 898656
 Avg_row_length: 29
    Data_length: 26787840
Max_data_length: 0
   Index_length: 9977856
      Data_free: 5242880
 Auto_increment: 1817490
    Create_time: 2018-09-14 16:11:06
    Update_time: 2018-09-30 17:54:12
     Check_time: NULL
      Collation: utf8mb4_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 

方式2：show create table user_id;

*************************** 1. row ***************************
       Table: user_id
Create Table: CREATE TABLE `userid` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `is_used` tinyint(4) NOT NULL DEFAULT '0',
  `user_id` int(11) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `is_used_idx` (`is_used`)
) ENGINE=InnoDB AUTO_INCREMENT=1817490 DEFAULT CHARSET=utf8mb4
1 row in set (0.01 sec)

5、查看表中字段的字符集

show full columns from 表名;

mysql> show full columns from recordinfo;
+---------------+---------------+--------------------+------+-----+-------------------+-------+---------------------------------+---------+
| Field         | Type          | Collation          | Null | Key | Default           | Extra | Privileges                      | Comment |
+---------------+---------------+--------------------+------+-----+-------------------+-------+---------------------------------+---------+
| uuid     | int(11)       | NULL               | NO   | PRI | NULL              |       | select,insert,update,references |         |
| current | int(11)       | NULL               | NO   | PRI | NULL              |       | select,insert,update,references |         |
| data   | varchar(4096) | utf8mb4_general_ci | NO   |     |                   |       | select,insert,update,references |         |
| replay        | blob          | NULL               | NO   |     | NULL              |       | select,insert,update,references |         |
| code   | int(11)       | NULL               | NO   | MUL | NULL              |       | select,insert,update,references |         |
| time          | timestamp     | NULL               | NO   |     | CURRENT_TIMESTAMP |       | select,insert,update,references |         |
+---------------+---------------+--------------------+------+-----+-------------------+-------+---------------------------------+---------+

三、设置字符集（已存在的库、表、字段）

1、设置字段字符集

alter table 表名 modify `字段名` varchar(64) CHARACTER SET utf8mb4 NOT NULL DEFAULT '' COMMENT '昵称';

2、设置表字符集

alter table  表名      default charset=utf8mb4;

3、设置库字符集

alter database 库名 default character set 'utf8mb4';

字符集优先级由高到低：字段——表——库

四、设置字符集(创建时指定字符集)

1、创建数据库

create database 库名 default character set=utf8mb4;

2、创建表

create table student(
id int not null auto_increment primary key,
name varchar(10) not null default '' comment '姓名'
) default character set='utf8mb4';

3、创建字段

create table student(
id int not null auto_increment primary key,
name varchar(10) character set utf8mb4  not null default '' comment '姓名'
) default character set='utf8mb4';

PS：

     创建库时，如果不指定字符集，则使用系统默认库字符集   

     创建表时，如果不指定字符集，则继承库的字符集  

     新增字段时，如果不指定字符集，则继承表的字符集

五、修改全局字符集

临时修改(mysql服务重启失效):

/*建立连接使用的编码*/
set character_set_connection=utf8;
/*数据库的编码*/
set character_set_database=utf8;
/*结果集的编码*/
set character_set_results=utf8;
/*数据库服务器的编码*/
set character_set_server=utf8;

set character_set_system=utf8;

set collation_connection=utf8;

set collation_database=utf8;

set collation_server=utf8;

永久修改:

修改配置文件，重启mysql服务

character-set-server=utf8mb4

[root@localhost ~]$ grep "utf8mb4" /etc/my.cnf
character-set-server=utf8mb4

注意:以上修改，只是对新增的库生效，已存在的库 表  字段不生效