Second Normal Form (2NF)

 Definition: In order to be in Second Normal Form, a relation must first fulfill the requirements to be in First Normal Form.  Additionally, each nonkey attribute in the relation must be functionally dependent upon the primary key.

Example: The following relation is in First Normal Form, but not Second Normal Form:

Order #	Customer	Contact Person	Total
1	Acme Widgets	John Doe	$134.23
2	ABC Corporation	Fred Flintstone	$521.24
3	Acme Widgets	John Doe	$1042.42
4	Acme Widgets	John Doe	$928.53

In the table above, the order number serves as the primary key.  Notice that  the customer and total amount are dependent upon the order number -- this data is specific to each order.  However, the contact person is dependent upon the customer.  An alternative way to accomplish this would be to create two tables:

Customer	Contact Person
Acme Widgets	John Doe
ABC Corporation	Fred Flintstone

 

Order #	Customer	Total
1	Acme Widgets	$134.23
2	ABC Corporation	$521.24
3	Acme Widgets	$1042.42
4	Acme Widgets	$928.53

The creation of two separate tables eliminates the dependency problem experienced in the previous case.  In the first table, contact person is dependent upon the primary key -- customer name.  The second table only includes the information unique to each order.