Why Use Both \'%\' and \'localhost\' When Defining MySQL User Hostnames?

MySQL User Hostnames: 'localhost' vs. '%'

In structuring a MySQL database, it's often necessary to create multiple users with distinct access privileges. One common debate arises when determining whether to specify a '%' or 'localhost' as the hostname for these users. This question delves into the difference between these two hostnames.

Problem:

A developer insists on creating four user accounts for two users (appuser and support):

• appuser@'%'
• appuser@'localhost'
• support@'%'
• support@'localhost'

The question here is why such a setup is necessary, considering the '%'-wildcard would seemingly cover 'localhost'.

Answer:

The hostname 'localhost' holds special significance in MySQL. Unlike '%'-wildcard, which applies to любых TCP/IP connections, 'localhost' exclusively refers to connections established via UNIX sockets (or named pipes on Windows systems).

In MySQL, the '%'-wildcard excludes localhost, making it necessary to explicitly specify it as a separate hostname. This setup allows for fine-grained control over user access from different network interfaces. By designating both '%' and 'localhost' for each user, the following is achieved:

• The '%' hostname grants access from any remote IP address.
• The 'localhost' hostname grants access from within the same server using UNIX sockets (or named pipes).

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