Searching for voters by address
OK Assuming you need the "Assigned Table" to support the many to many relationship of a voter to address.

`assigned_id` int(11) NOT NULL AUTO_INCREMENT,
`voter_id` int(11) NOT NULL,
`address_id` int(11) NOT NULL,
PRIMARY KEY (`assigned_id`)


You don't need assigned_id. Remove this. The primary key is (voter_id, address_id)