Columns do not contain more than one telephone number in this design. Instead, each Customer-to-Telephone Number link appears on its own row. Using Customer ID as key, a "one-to-many" relationship exists between the name and the number tables. A row in the "parent" table, Customer Name, can be associated with many telephone number rows in the "child" table, Customer Telephone Number, but each telephone number belongs to one, and only one customer. (In the "real" world, this would not be a good assumption.) It is worth noting that this design meets the additional requirements for second and third normal form.