Adminer is a database administration tool that allows viewing and editing of databases tables, routines, triggers, etc. It also allows running SQL statements to import data, make bulk changes, or perform other complex operations. It is similar in function to phpMyAdmin. It is intended for use by developers and those who have had experience with databases.
This plugin provides a secure connection to your WordPress database, limited to that which is saved in your WordPress configuration, and access is granted only to logged-in accounts that possess the edit_plugins capability (normally admins). This ensures it can only used by those who already have enough privilege to pose a risk to the installation. Each and every request to Adminer will first be authenticated using your WordPress session. Some security plugins impose extra restrictions on admin sessions, so this plugin may not work if you have one installed.
Note that any other databases on the same host and protected by the same credentials will also be accessible in Adminer. This is how databases operate and not a limitation of Adminer nor this plugin. If other databases need different access restrictions, they should have separate credentials.