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Lesson 6
Objective |
Limitations of 1NF Describe the limitations of 1st normal form. |
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Translating a table into 1NF alleviates much of the data redundancy and wasted space of a table that has not been normalized. First
normal form is only a first step to good design. It is still possible for a table in 1NF to be designed inefficiently. Consider the
following relation:
You can begin to address these problems by putting your relations into second normal form.
Order (CustID, CustName, Address, Phone, OrderDate, OrderNo, ItemNo, Title, Price, Shipped) The relation has no repeating groups and is, therefore, in 1NF. But the relation's design is still inefficient. First, the relation describes four entities: Customers (CustID, CustName, Address, Phone), Orders (OrderDate, OrderNo), Item (ItemNo, Title, Price), and order Line Items (OrderNo, ItemNo, Shipped). In this relation, a customer's personal information will be repeated in every record referring to an order the customer placed. As noted earlier, repetition increases the amount of time it takes to update that information and makes it more likely that an update will be missed, causing inconsistencies in the database. Second, the relation'sconcatenated primary key of OrderNo and ItemNo means that:
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