This isn't really a PHP issue.
The first approach you can do is to not flag the address as unique and allow multiple inserts. This only works if the logic of the design allows a many to many relationship. This can then accept a count.
Another approach would be to simply use an INSERT ON DUPLICATE KEY UPDATE syntax to issue an update when it finds a duplicate. The documentation for that is here: http://dev.mysql.com/doc/refman/5.0/...duplicate.html