Granting rights to additional MySQL database causing issues

Question

I have a user \'myuser\' and two databases. \'db1\' and \'db2\'.

\'myuser\' already has rights to use db1

Answer 1

MySQL identifies a user by BOTH the username and the host. When MySQL does the authentication at login, MySQL first looks for a hostname that is an exact match. If it doesn't find an exact match, then it looks for a host containing a '%' wildcard.

When you did the GRANT ... TO myuser@localhost, MySQL created a new user (with no password, because there was no IDENTIFIED BY given in the statement.

Then what happened, when you attempted to login as myuser from the localhost, mysqld tried to find an entry that matched 'myuser'@'localhost' in the mysql.user table and it found it. And the session got the privileges assigned to that user.

(To be a little more precise, mysqld doesn't really look at the contents of the mysql.user table, what it really looks at the in-memory structure, which was populated from the table when it was built. A rebuild of the memory structure is triggered by a GRANT, a REVOKE or a FLUSH PRIVILEGES statement.)

What was happening BEFORE you added that new user, mysqld was looking for an exact match on user and hostname, and didn't find one. But it did find an entry with the '%' wildcard, so it matched to that, so the session got all the privileges granted to the 'myuser'@'%' user.

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The two users 'u'@'%' and 'u'@'localhost' are separate and distinct from each other. Privileges must be granted to each user individually. Any privileges granted to 'u'@'%' apply ONLY to that user and NOT to 'u'@'localhost'.