Database Reference
In-Depth Information
ees are already accustomed to identifying themselves by their assigned numbers. Using
E
MPLOYEE
N
UMBER
makes perfect sense, so you select it as the primary key for the table.
Figure 8.12. The EMPLOYEES table structure in the Mike's Bikes database
Now you perform one final task before you designate E
MPLOYEE
N
UMBER
as the official
primarykeyofthetable:Youmakeabsolutelycertainthatitexclusivelyidentifiesthevalue
of each field within a given record. So you test E
MPLOYEE
N
UMBER
by following these
steps.
1.
Load the EMPLOYEES table with sample data.
2.
Select a record for test purposes and note the current value of E
MPLOYEE
N
UMBER
.
3.
Examine the value of the first field (the one immediately after E
MPLOYEE
N
UMBER
)
and ask yourself this question:
Does this primary key value
exclusively
identify the current value of
<field-
name>?
a.
If the answer is yes, move to the next field and repeat the question.
