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MySQL字符集和排序方式

Jun 07, 2016 pm 03:12 PM
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欢迎进入Linux社区论坛,与200万技术人员互动交流 >>进入 MySQL的字符串分为两大类: 1)二进制字符串:即一串字节序列,对字节的解释不涉及字符集,因此它没有字符集和排序方式的概念 2)非二进制字符串:由字符构成的序列,字符集用来解释字符串的内容,排

欢迎进入Linux社区论坛,与200万技术人员互动交流 >>进入

  MySQL的字符串分为两大类:

  1)二进制字符串:即一串字节序列,对字节的解释不涉及字符集,因此它没有字符集和排序方式的概念

  2)非二进制字符串:由字符构成的序列,字符集用来解释字符串的内容,排序方式决定字符的大小

  字符集和排序方式

  字符集和排序方式的关系是这样的:一个字符集可以有一个或多个排序方式,有一个默认的排序方式,我们可以通过以下例子说明:

MySQL字符集和排序方式

 

  从上例中我们可以看出字符集gbk有两个排序方式(分别为gbk_chinese_ci何gbk_bin),其中默认的排序方式为gbk_chinese_ci.

  排序方式的命名规则为:字符集名字_语言_后缀,其中各个典型后缀的含义如下:

  1)_ci:不区分大小写的排序方式

  2)_cs:区分大小写的排序方式

  3)_bin:二进制排序方式,大小比较将根据字符编码,不涉及人类语言,因此_bin的排序方式不包含人类语言

  因此,gbk_chinese_ci排序方式就表示:字符集为gbk,人类语言使用中文来比较大小,比较时区分大小写。

  常用函数

  字符集引导

  字符集引导可以让MySQL指定一种字符集来解释字符常量,其语法为:

  _charset str

  如:

  _utf8 'ABCD'   表示以utf8字符集来介绍字符串常量'ABCD'

  字符集转换

  convert()函数可以把一个字符串转换成指定字符集,其语法为:

  convert(str using charset)

  如 convert('ABCD' using utf8)  表示把'ABCD'的字符集转换成uft8

  length()函数  --返回字节的长度

  char_length()  --返回字符长度

  与字符集有关的系统变量

  通过以下语句可以查看与字符集有关的系统变量:

MySQL字符集和排序方式

 

  它们的含义如下:

  character_set_system:MySQL数据库标识符使用的字符集,永远是utf8

  character_set_server和collation_server:服务器的默认字符集和排序方式

  character_set_database和collation_database:当前数据库的默认字符集和排序方式

  以下三个变量将影响客户端和服务器之间的通信:

  character_set_client:客户端向服务器发送SQL语句使用的字符集

  character_set_results:服务器向客户端返回结果时使用的字符集

  character_set_connection:如果它和character_set_client不同,从客户端发来的SQL语句将转换为它指定的字符集

  默认情况下,上述三个变量都设为为相同的值,如果某个客户端想使用另一种字符集与服务器通信,可以修改它们,如:

  [sql]

  set character_set_client = utf8;

  set character_set_results = utf8;

  set character_set_connection = utf8;

  或者,更简单的方法是使用如下一条语句也能达到相同的效果:

  [sql]

  set names 'utf8';

MySQL字符集和排序方式

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