Database Reference
In-Depth Information
Figure 8.5. Which candidate key should become the primary key of the
EMPLOYEES table?
Either of the candidate keys you identified within the table could serve as the primary key.
You might decide to choose E
MPLOYEE
ID if everyone in the organization is accustomed to
using this number as a means of identifying employees in items such as tax forms and em-
ployee benefits programs. The candidate key you ultimately choose becomes the primary
key of the table and is governed by the
Elements of a Primary Key
. These elements are
exactly the same as those for the candidate key, and you should enforce them to the letter.
For the sake of clarity, here are the Elements of a Primary Key:
Elements of a Primary Key
• It cannot be a multipart field.
• It must contain unique values.
• It cannot contain null values.
• Its value cannot cause a breach of the organization's security or privacy rules.
