查看数据库支持的字符集:SHOW CHARACTER SET

查看数据库支持的排序规则:SHOW COLLATION

字符集(Character Sets)

下表是 MySQL 中八个可能影响到字符集的系统变量,其中有几个如果配置不当可能会乱码问题,需重点关注:

变量 默认值 描述
character_set_client utf8 The character set for statements that arrive from the client.
character_set_connection utf8 The character set used for literals specified without a character set introducer and for number-to-string conversion.
character_set_database latin1 The character set used by the default database.
character_set_filesystem binary The file system character set.
character_set_results utf8 The character set used for returning query results to the client. This includes result data such as column values, result metadata such as column names, and error messages.
character_set_server latin1 The server’s default character set.
character_set_system utf8 The character set used by the server for storing identifiers.
character_sets_dir The directory where character sets are installed.

可以通过下图来了解 MySQL 内部字符集转换过程:

MySQL Character Set

  1. MySQL 收到请求时将请求数据从 character_set_client 转换为 character_set_connection
  2. 进行内部操作前将请求数据从 character_set_connection 转换为内部操作字符集,步骤如下:
    1. 使用每个数据字段的 CHARACTER SET 设定值;
    2. 若上述值不存在,则使用对应数据表的字符集设定值;
    3. 若上述值不存在,则使用对应数据库的字符集设定值;
    4. 若上述值不存在,则使用 character_set_server 设定值。
  3. 最后将操作结果从内部操作字符集转换为 character_set_results

而系统变量 character_set_database 主要用来设置默认创建数据库的编码格式,如果在创建数据库时没有设置编码格式,就按照这个格式设置,如下:

1
CREATE DATABASE `testdb` /*!40100 DEFAULT CHARACTER SET latin1 */

从而影响到建表时默认的字符集:

1
2
3
CREATE TABLE `test` (
`name` varchar(255) NOT NULL DEFAULT ''
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

从而影响到中文字符的插入:

1
2
3
INSERT INTO test values ('你好');

[Err] 1366 - Incorrect string value: '\xE4\xBD\xA0\xE5\xA5\xBD' for column 'name' at row 1

配置说明

1
2
3
4
5
6
7
8
9
10
11
12
13
14
[mysqld]
# 影响系统变量 character_set_database 和 character_set_server
character-set-server = utf8
collation-server = utf8_unicode_ci
init-connect = 'SET NAMES utf8'

# 创建新表时将使用的默认存储引擎
default-storage-engine=INNODB

[client]
default-character-set = utf8

[mysql]
default-character-set = utf8

配置后,需要重启服务:

1
2
net stop mysql
net start mysql

之后,通过命令 SHOW VARIABLES LIKE '%character%' 查看结果:

1
2
3
4
5
6
7
8
9
10
11
12
+--------------------------+----------+
| 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 | ... |
+--------------------------+----------+

如果在创建数据库之前,没有在配置文件中配置好默认字符集,可以通过 SET 命令进行修改。

配置好后,建库结果如下:

1
CREATE DATABASE `testdb` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci */

排序规则(Collations)

参考

https://dev.mysql.com/doc/refman/5.7/en/charset.html

https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html

charset