Pregunta de entrevista de BuildASign.com

You are given a database that has a single table with six columns: FirstName, LastName, ContactType, PhoneNumber, Email, CreatedOn. Data may look like: John | Doe | Work | 8881234567 | johndoe@email.com | Dec 22, 2012 John | Doe | Cell | 8882345678 | johndoe@email.com | Dec 23, 2012 The only clue given was the question, "How can we be sure that those two John Doe rows are the same person?" With that, redesign the database for better reliability and performance.