The DBA denormalized some of the data in the TAL Distributors database to improve performance, and one of the resulting tables is the following:

Question:

The DBA denormalized some of the data in the TAL Distributors database to improve performance, and one of the resulting tables is the following:

Customer (CustomerNum, CustomerName, Street, City, State, PostalCode, Balance, CreditLimit, RepNum, RepName)

Which field or fields cause the table to no longer be in third normal form? In which normal form is the denorma-lized table?

Answer:

One of the tables from the Premier Products database after the DBA has denormalized the database is

Customer(CustomerNum, CustomerName, Street, City, State,

Zip, Balance,CreditLimit, RepNum, RepName)

In the Customer table, CustomerNum is the primary key.

First normal form

• According to the first normal form, the table should not contain repeating groups.

• Customer table is satisfying the first normal form as there are no repeating groups.

Second Normal form

• According to the Second Normal form, a table must be in first normal form and any non-key attribute must depend only on the primary key.

• In the Customer table, the primary key is CustomerNum.

• The non-key attributes CustomerName, Street, City, State, Zip, Balance, CreditLimit are dependent on CustomerNum.

• The non-key attribute RepName is dependent on RepNum and not on the primary key.

• Hence Customer table is not in Second Normal Form

Third Normal form

• According to the Third Normal form, a table must be in second normal form and any non-key attribute should not describe any other non-key attribute.

• As the table Customer is not in second normal form, it cannot be in third normal form.

• Hence Customer table is not in the Third Normal Form.

Fields that caused the Customer table to no longer be in the Third Normal form are RepNum and RepName.

The denormalized table Customer is in first normal form.

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