Lesson 6 | Limitations of 1NF |
Objective | Describe the limitations of first normal form. |
Limitations of First Normal Form
Concatenated Primary Key
Second, the relation's
concatenated primary key of OrderNo and ItemNo means that:
- You must know at least one item in a customer's order to enter information about that customer.
- You can not enter information about an item until that item has been ordered once.
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Deleting a customer’s only order deletes all information about that customer.
(Remember, a customer's contact information is stored along with their orders, not separately. If you delete from your database the only order a customer has placed, you also delete that customer's contact information.
- Deleting from the database the only order for an item deletes all information about that item.
You can begin to address these problems by putting your relations into
second normal form.
- second normal form (2NF): A table is in second normal form when every attribute is functionally dependent on the entire primary key.
- concatenated primary key: A primary key made up of more than one field.
The next lesson defines second normal form.