Why only grant usage permissions can be deleted and modified

Log in to the remote database on 192.168.0.1 with Dbuser:


Show grants;
Show

GRANT USAGE on * * to ' dbuser ' @ ' 192.168.0.1 ' identified by PASSWORD ' *fe63xxxxxxxxxxxxx1c16a ' only this one,

Dbuser This user only usage permissions, check the next MySQL manual,mysql usage permissions is empty permissions, the default create user permissions, can only connect the library, nothing can dry, but this user can be database table SELECT, INSERT, Update,delete, what's going on?

After the investigation and discovery,

Show grants shows the permissions of this user, but if there are user,db data inconsistencies in these permission tables,
It is not so smart, because there were [email protected]% users, assigned permissions, and later deleted from the user table,
Without the drop user, the user table is not available, but the DB table permission is still there, and another user [email protected] accesses the DB table to view the permissions.
Just mapping to the [email protected]% This user's permission, so you can delete and change the search, but with show grants for user [email protected] will only display and it
The right to exactly match, and does not introduce% This user's permissions, so all operations with the command, can guarantee the consistency of the permission table, otherwise it is easy to find the problem.

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Why only grant usage permissions can be deleted and modified