Databases Reference
In-Depth Information
Customer
CustomerNum
CustomerName
Balance
CreditLimit
RepNum
LastName
FirstName
148
Al's Appliance
$6,550.00
$7,500.00
20
Kaiser
Valerie
and Sport
282
Brookings Direct
$431.50
$10,000.00
35
Hull
Richard
356
Ferguson's
$5,785.00
$7,500.00
65
Perez
Juan
164
408
The Everything
$5,285.25
$5,000.00
35
Hull
Richard
Shop
462
Bargains Galore
$3,412.00
$10,000.00
65
Perez
Juan
524
Kline's
$12,762.00
$15,000.00
20
Kaiser
Valerie
608
Johnson's
$2,106.00
$10,000.00
65
Perez
Juan
Department
Store
687
Lee's Sport
$2,851.00
$5,000.00
35
Hull
Richard
and Appliance
725
Deerfield's
$248.00
$7,500.00
35
Hull
Richard
Four Seasons
842
All Season
$8,221.00
$7,500.00
20
Kaiser
Valerie
Customer
Rep
CustomerNum
LastName
FirstName
CustomerNum
CustomerName
Balance
CreditLimit
RepNum
148
Al's Appliance
$6,550.00
$7,500.00
20
148
Kaiser
Valerie
and Sport
282
Hull
Richard
282
Brookings Direct
$431.50
$10,000.00
35
356
Perez
Juan
356
Ferguson's
$5,785.00
$7,500.00
65
408
Hull
Richard
408
The Everything
$5,285.25
$5,000.00
35
462
Perez
Juan
Shop
524
Kaiser
Valerie
462
Bargains Galore
$3,412.00
$10,000.00
65
608
Perez
Juan
524
Kline's
$12,762.00
$15,000.00
20
687
Hull
Richard
608
Johnson's
$2,106.00
$10,000.00
65
Department Store
725
Hull
Richard
687
Lee's Sport
$2,851.00
$5,000.00
35
842
Kaiser
Valerie
and Appliance
725
Deerfield's Four
$248.00
$7,500.00
35
Seasons
842
All Season
$8,221.00
$7,500.00
20
FIGURE 5-13
Incorrect decomposition of the Customer table
Consider, for example, the redundancy in the storage of sales reps' names, the problem encountered in
changing the name of a sales rep, and the difficulty of adding a new sales rep who represents no customers. In
addition, because the rep number and names are in different tables, you have actually
split a functional
dependence across two different tables
. Thus, this seemingly valid decomposition is definitely not a desir-
able way to create third normal form tables.
