If you would use IPtables to allow only a certain IP for a database won't work if you access the database via HTTP like PHPmyadmin. With IPtables you can block incoming connections (and outgoing / forwarding) and since phpmyadmin (if used) will be localhost that won't work. So with IPtables look out since it's just a firewall :)

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Nunchaku! Who doesn't like martial arts? =)