Account name syntax is 'user_name'@'host_name'.

The @'host_name' part is optional. An account name consisting only of a user name is equivalent to 'user_name'@'%'. For example, 'me' is equivalent to 'me'@'%'.

The user name and host name need not be quoted if they are legal as unquoted identifiers. Quotes must be used if a user_name string contains special characters (such as space or -), or a host_name string contains special characters or wildcard characters (such as . or %). For example, in the account name 'test-user'@'%.com', both the user name and host name parts require quotes.

Quote user names and host names as identifiers or as strings, using either backticks (`), single quotation marks ('), or double quotation marks ("). For string-quoting and identifier-quoting guidelines, see Section 9.1.1, “String Literals”, and Section 9.2, “Schema Object Names”.

The user name and host name parts, if quoted, must be quoted separately. That is, write 'me'@'localhost', not 'me@localhost'. The latter is actually equivalent to 'me@localhost'@'%'.

A reference to the CURRENT_USER or CURRENT_USER() function is equivalent to specifying the current client's user name and host name literally.

The user table contains one row for each account. The User and Host columns store the user name and host name. This table also indicates which global privileges the account has.

Other grant tables indicate privileges an account has for databases and objects within databases. These tables have User and Host columns to store the account name. Each row in these tables associates with the account in the user table that has the same User and Host values.

For access-checking purposes, comparisons of User values are case-sensitive. Comparisons of Host values are not case-sensitive.

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:

Suppose that a host on the local network has a fully qualified name of host1.example.com. If DNS returns name lookups for this host as host1.example.com, use that name in account host values. If DNS returns just host1, use host1 instead.

If DNS returns the IP address for a given host as 198.51.100.2, that matches an account host value of 198.51.100.2 but not 198.051.100.2. Similarly, it matches an account host pattern like 198.51.100.% but not 198.051.100.%.