MySQL的字符集和乱码问题

1.字符集知识

#概述

.字符集是一套文字符号及其编码、比较规则的集合，第一个计算机字符串ASC2
.mysql数据库字符集包括字符集(character)和 校对规则，其中字符集使用来定义mysql数据字符串的存储方式，校对规则是定义比较字符串的方式

#扩展

#字符编码:就是人类使用的英文字母、汉字、特殊符号等信息，通过转换规则，将其转换为计算机可以识别的二进制数字的一种编码方式

#mysql数据库常见字符集

常用字符集　    长度    说明
GBK　　　  　　      不是国际标准
UTF-   　　　      中英文混合的环境，建议使用
Latin1  　　　      mysql默认字符集
Utf8mb4 　　　      Utf- unicode

#选择合适的字符集

.处理各种各样的文字，发布到不同语言国家地区，应该选择Unicode字符集，在mysql里面就是utf-(每个汉字三个字节)
.如果只需要支持中文，并且数据量大，性能要求高，可选择GBK(定长，每个汉字双字节)
.处理移动互联网业务，可使用utf8mb4字符集

#查看系统的字符集

[root@cots3 ~]# mysql -uroot -p -e "show character set;"
Enter password:
+----------+---------------------------------+---------------------+--------+
| Charset  | Description                     | Default collation   | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese        | big5_chinese_ci     |       |
| dec8     | DEC West European               | dec8_swedish_ci     |       |
| cp850    | DOS West European               | cp850_general_ci    |       |
| hp8      | HP West European                | hp8_english_ci      |       |
| koi8r    | KOI8-R Relcom Russian           | koi8r_general_ci    |       |
| latin1   | cp1252 West European            | latin1_swedish_ci   |       |
| latin2   | ISO - Central European     | latin2_general_ci   |       |
| swe7     | 7bit Swedish                    | swe7_swedish_ci     |       |
| ascii    | US ASCII                        | ascii_general_ci    |       |
| ujis     | EUC-JP Japanese                 | ujis_japanese_ci    |       |
| sjis     | Shift-JIS Japanese              | sjis_japanese_ci    |       |
| hebrew   | ISO - Hebrew               | hebrew_general_ci   |       |
| tis620   | TIS620 Thai                     | tis620_thai_ci      |       |
| euckr    | EUC-KR Korean                   | euckr_korean_ci     |       |
| koi8u    | KOI8-U Ukrainian                | koi8u_general_ci    |       |
| gb2312   | GB2312 Simplified Chinese       | gb2312_chinese_ci   |       |
| greek    | ISO - Greek                | greek_general_ci    |       |
| cp1250   | Windows Central European        | cp1250_general_ci   |       |
| gbk      | GBK Simplified Chinese          | gbk_chinese_ci      |       |
| latin5   | ISO - Turkish              | latin5_turkish_ci   |       |
| armscii8 | ARMSCII- Armenian              | armscii8_general_ci |       |
| utf8     | UTF- Unicode                   | utf8_general_ci     |       |
| ucs2     | UCS- Unicode                   | ucs2_general_ci     |       |
| cp866    | DOS Russian                     | cp866_general_ci    |       |
| keybcs2  | DOS Kamenicky Czech-Slovak      | keybcs2_general_ci  |       |
| macce    | Mac Central European            | macce_general_ci    |       |
| macroman | Mac West European               | macroman_general_ci |       |
| cp852    | DOS Central European            | cp852_general_ci    |       |
| latin7   | ISO - Baltic              | latin7_general_ci   |       |
| utf8mb4  | UTF- Unicode                   | utf8mb4_general_ci  |       |
| cp1251   | Windows Cyrillic                | cp1251_general_ci   |       |
| utf16    | UTF- Unicode                  | utf16_general_ci    |       |
| utf16le  | UTF-16LE Unicode                | utf16le_general_ci  |       |
| cp1256   | Windows Arabic                  | cp1256_general_ci   |       |
| cp1257   | Windows Baltic                  | cp1257_general_ci   |       |
| utf32    | UTF- Unicode                  | utf32_general_ci    |       |
| binary   | Binary pseudo charset           | binary              |       |
| geostd8  | GEOSTD8 Georgian                | geostd8_general_ci  |       |
| cp932    | SJIS for Windows Japanese       | cp932_japanese_ci   |       |
| eucjpms  | UJIS for Windows Japanese       | eucjpms_japanese_ci |       |
| gb18030  | China National Standard GB18030 | gb18030_chinese_ci  |       |
+----------+---------------------------------+---------------------+--------+

#过滤出常用

[root@cots3 ~]# mysql -uroot -p -e "show character set;" |egrep  "Charset|gbk|utf8|latin1" | awk '{print $0}'
Enter password:
Charset    Description           Default collation    Maxlen
latin1    cp1252 West European    latin1_swedish_ci
gbk       GBK Simplified Chinese  gbk_chinese_ci
utf8      UTF- Unicode           utf8_general_ci
utf8mb4   UTF- Unicode           utf8mb4_general_ci    

#查看字符集对应校对规则

mysql> show collation like 'utf8%';
+--------------------------+---------+-----+---------+----------+---------+
| Collation                | Charset | Id  | Default | Compiled | Sortlen |
+--------------------------+---------+-----+---------+----------+---------+
| utf8_general_ci          | utf8    |   | Yes     | Yes      |        |
| utf8_bin                 | utf8    |   |         | Yes      |        |
| utf8_unicode_ci          | utf8    |  |         | Yes      |        |
| utf8_icelandic_ci        | utf8    |  |         | Yes      |        |
| utf8_latvian_ci          | utf8    |  |         | Yes      |        |
| utf8_romanian_ci         | utf8    |  |         | Yes      |        |
| utf8_slovenian_ci        | utf8    |  |         | Yes      |        |
| utf8_polish_ci           | utf8    |  |         | Yes      |        |
| utf8_estonian_ci         | utf8    |  |         | Yes      |        |
| utf8_spanish_ci          | utf8    |  |         | Yes      |        |
| utf8_swedish_ci          | utf8    |  |         | Yes      |        |
| utf8_turkish_ci          | utf8    |  |         | Yes      |        |
| utf8_czech_ci            | utf8    |  |         | Yes      |        |
| utf8_danish_ci           | utf8    |  |         | Yes      |        |
| utf8_lithuanian_ci       | utf8    |  |         | Yes      |        |
| utf8_slovak_ci           | utf8    |  |         | Yes      |        |
| utf8_spanish2_ci         | utf8    |  |         | Yes      |        |
| utf8_roman_ci            | utf8    |  |         | Yes      |        |
| utf8_persian_ci          | utf8    |  |         | Yes      |        |
| utf8_esperanto_ci        | utf8    |  |         | Yes      |        |
| utf8_hungarian_ci        | utf8    |  |         | Yes      |        |
| utf8_sinhala_ci          | utf8    |  |         | Yes      |        |
| utf8_german2_ci          | utf8    |  |         | Yes      |        |
| utf8_croatian_ci         | utf8    |  |         | Yes      |        |
| utf8_unicode_520_ci      | utf8    |  |         | Yes      |        |
| utf8_vietnamese_ci       | utf8    |  |         | Yes      |        |
| utf8_general_mysql500_ci | utf8    |  |         | Yes      |        |
| utf8mb4_general_ci       | utf8mb4 |   | Yes     | Yes      |        |
| utf8mb4_bin              | utf8mb4 |   |         | Yes      |        |
| utf8mb4_unicode_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_icelandic_ci     | utf8mb4 |  |         | Yes      |        |
| utf8mb4_latvian_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_romanian_ci      | utf8mb4 |  |         | Yes      |        |
| utf8mb4_slovenian_ci     | utf8mb4 |  |         | Yes      |        |
| utf8mb4_polish_ci        | utf8mb4 |  |         | Yes      |        |
| utf8mb4_estonian_ci      | utf8mb4 |  |         | Yes      |        |
| utf8mb4_spanish_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_swedish_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_turkish_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_czech_ci         | utf8mb4 |  |         | Yes      |        |
| utf8mb4_danish_ci        | utf8mb4 |  |         | Yes      |        |
| utf8mb4_lithuanian_ci    | utf8mb4 |  |         | Yes      |        |
| utf8mb4_slovak_ci        | utf8mb4 |  |         | Yes      |        |
| utf8mb4_spanish2_ci      | utf8mb4 |  |         | Yes      |        |
| utf8mb4_roman_ci         | utf8mb4 |  |         | Yes      |        |
| utf8mb4_persian_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_esperanto_ci     | utf8mb4 |  |         | Yes      |        |
| utf8mb4_hungarian_ci     | utf8mb4 |  |         | Yes      |        |
| utf8mb4_sinhala_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_german2_ci       | utf8mb4 |  |         | Yes      |        |
| utf8mb4_croatian_ci      | utf8mb4 |  |         | Yes      |        |
| utf8mb4_unicode_520_ci   | utf8mb4 |  |         | Yes      |        |
| utf8mb4_vietnamese_ci    | utf8mb4 |  |         | Yes      |        |
+--------------------------+---------+-----+---------+----------+---------+
 rows in set (0.01 sec)

#查看系统默认设置的字符集

mysql> show variables like "character_set%";
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |  #客户端字符集
| character_set_connection | utf8                       |  #连接字符集
| character_set_database   | latin1                     |  #数据库字符集，配置文件指定或库表指定
| character_set_filesystem | binary                     |  #文件系统字符集
| character_set_results    | utf8                       |  #返回结果字符集
| character_set_server     | latin1                     |  #服务器字符集，配置文件指定或库表指定
| character_set_system     | utf8                       |  #系统字符集
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
 rows in set (0.00 sec)

#提示：默认情况下character_set_client,character_set_connection,character_set_results三者的字符集和系统的字符集一致，如果mysql不指定

#查看系统字符集

[root@cots3 ~]# cat /etc/locale.conf
LANG="en_US.UTF-8"
[root@cots3 ~]# echo $LANG
en_US.UTF-

#指定字符集进行登录数据库

[root@ctos3 ~]# mysql -uroot -p --default-character-set=latin1;
Enter password: 

mysql> show variables like 'character_set%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | latin1                     |
| character_set_connection | latin1                     |
| character_set_database   | latin1                     |
| character_set_filesystem | binary                     |
| character_set_results    | latin1                     |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
 rows in set (0.00 sec)
#提示：将原来set_client,set_connection,set_results的字符集更改了

2.乱码问题

#如果我们设置的字符集不相同的话，就会可能出现乱码

#保证不乱码思想：统一字符集，中英文的环境建议选择utf8

#保证不乱码的关键，保证以下几个统一

.Linux操作系统
.操作系统客户端连接(xshell,ssh)
.mysql服务端
.mysql客户端
.mysql库表
.开发的程序字符集

#例子：统一设置成utf8

#1.Linux系统

[root@mysql- ~]# cat /etc/locale.conf     #centos7系统
LANG="en_US.UTF-8"
[root@mysql- ~]# cat /etc/sysconfig/il8n   #centos6系统查看
LANG="en_US.UTF-8"

[root@mysql- ~]# echo $LANG
zh_CN.UTF-
#提示：使用SecureCRT或xshell连接服务器的也要更改

#2.mysql服务端

#在/etc/my.cnf的mysqld模块里面更改
[mysqld]
character-set-server=utf8

#3.mysql客户端

#在/etc/my.cnf文件里面添加客户端模块，无需重启
[client]
default-character-set=utf8

#4.mysql库表，一般上面几个改完，库表都会随着mysql的字符集

mysql> create database data_utf8 character set=utf8;
Query OK,  row affected (0.01 sec)

mysql> show create database data_utf8\G;
*************************** . row ***************************
       Database: data_utf8
Create Database: CREATE DATABASE `data_utf8` /*!40100 DEFAULT CHARACTER SET utf8 */
 row in set (0.00 sec)

#5.开发的程序字符集

#在下载的时候选择UTF8