帐户名语法是 . 'user_name'@'host_name'

该 部分是可选的。仅由用户名组成的帐户名等同于 . 例如，相当于 . @'host_name''user_name'@'%''me''me'@'%'

如果用户名和主机名作为未加引号的标识符是合法的，则不需要加引号。user_name如果字符串包含特殊字符（例如空格或-），或者 host_name字符串包含特殊字符或通配符（例如 .或），则必须使用引号 %。例如，在 account name'test-user'@'%.com'中，用户名和主机名部分都需要引号。

使用反引号 ( `)、单引号 ( ') 或双引号 ( ") 将用户名和主机名作为标识符或字符串引用。有关字符串引用和标识符引用指南，请参阅 第 9.1.1 节，“字符串文字”和 第 9.2 节，“模式对象名称”。

如果引用用户名和主机名部分，则必须单独引用。即写 'me'@'localhost'，不 写'me@localhost'。后者实际上相当于'me@localhost'@'%'.

CURRENT_USER 对or函数 的引用CURRENT_USER()等同于按字面指定当前客户端的用户名和主机名。

该user表包含每个帐户一行。和列存储用户名和主机名User。 Host此表还指示该帐户具有哪些全局权限。

其他授权表指示帐户对数据库和数据库中的对象具有的权限。这些表有 User和Host列来存储帐户名称。user这些表中的每一行都与表中具有相同User和Host 值 的帐户相关联。

出于访问检查目的，用户值的比较区分大小写。主机值的比较不区分大小写。

A host value can be a host name or an IP address (IPv4 or IPv6). The name 'localhost' indicates the local host. The IP address '127.0.0.1' indicates the IPv4 loopback interface. The IP address '::1' indicates the IPv6 loopback interface.

The % and _ wildcard characters are permitted in host name or IP address values. These have the same meaning as for pattern-matching operations performed with the LIKE operator. For example, a host value of '%' matches any host name, whereas a value of '%.mysql.com' matches any host in the mysql.com domain. '198.51.100.%' matches any host in the 198.51.100 class C network.

Because IP wildcard values are permitted in host values (for example, '198.51.100.%' to match every host on a subnet), someone could try to exploit this capability by naming a host 198.51.100.somewhere.com. To foil such attempts, MySQL does not perform matching on host names that start with digits and a dot. For example, if a host is named 1.2.example.com, its name never matches the host part of account names. An IP wildcard value can match only IP addresses, not host names.

For a host value specified as an IPv4 address, a netmask can be given to indicate how many address bits to use for the network number. Netmask notation cannot be used for IPv6 addresses.

The syntax is host_ip/netmask. For example:

CREATE USER 'david'@'198.51.100.0/255.255.255.0';

This enables david to connect from any client host having an IP address client_ip for which the following condition is true:

client_ip & netmask = host_ip

That is, for the CREATE USER statement just shown:

client_ip & 255.255.255.0 = 198.51.100.0

IP addresses that satisfy this condition range from 198.51.100.0 to 198.51.100.255.

A netmask typically begins with bits set to 1, followed by bits set to 0. Examples:

假设本地网络上的主机具有完全限定名称host1.example.com. 如果 DNS 将此主机的名称查找返回为 host1.example.com，请在帐户主机值中使用该名称。如果 DNS 仅返回host1，请 host1改用。

如果 DNS 返回给定主机的 IP 地址为 198.51.100.2，则匹配帐户主机值198.51.100.2但不 匹配198.051.100.2。同样，它匹配一个帐户主机模式，如198.51.100.%但不是198.051.100.%。