Why Use Both \'%\' and \'localhost\' When Creating MySQL Users?

Understanding the Need for Multiple Host Specifications

When creating MySQL users, it's common to encounter the question of whether to use % as the host or specify both % and localhost. This debate recently emerged in a query regarding the need for four accounts for appuser and support:

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

The Wildcard Host (%) vs. Localhost

The question arose because the developer insisted on creating four accounts, while the database administrator argued that using % as the host would suffice. However, as the answer correctly states:

localhost is a Special Case:

In MySQL, localhost refers to connections made via UNIX sockets or named pipes (on Windows). These connections are distinct from TCP/IP socket connections.

Wildcard Host Excludes Localhost:

Using % as the host allows connections from all hosts except localhost. This exclusion necessitated the explicit specification of localhost in addition to % to accommodate connections from local applications.

Therefore, the developer's request was justified in order to ensure that both local and remote applications could access the database with appropriate privileges.

In conclusion, it's essential to understand the special role of localhost in MySQL and the difference between host and IP address when managing user permissions. By correctly specifying both % and localhost, database administrators can grant access to users from various sources while maintaining security.

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