The reason is to eliminate those that were not duplicated. E.g. If you have:
John Maxwell 111 crogo rd. Albany, NY 62000
John Maxwell 111 crogo rd. Albany, NY 62000
David Taylor 105 Baylor Dr. Baltimore, MD 23100
Jeff Daniels 200 crogo rd. Richmond, VA 34511
Jeff Daniels 1 Mayberry Dr. Richmond, VA 34511
Mary Kay 50 crogo rd. St. Louis, MO 63136
The result should be:
John Maxwell 111 crogo rd. Albany, NY 62000
John Maxwell 111 crogo rd. Albany, NY 62000
Jeff Daniels 200 crogo rd. Richmond, VA 34511
Jeff Daniels 1 Mayberry Dr. Richmond, VA 34511
Dulicates in FName, LName, and Zipcode.
Thanks.