Database Reference
In-Depth Information
Figure 8.8. The EMPLOYEES table with designated primary and alternate keys
Non-keys
A non-key is a field that does not serve as a candidate, primary, alternate, or foreign key.
Its sole purpose is to represent a characteristic of the table's subject, and its value is de-
termined by the primary key. There is no particular designation for a non-key, so you don't
need to mark it in the table structure.
Table-Level Integrity
This type of integrity is a major component of overall data integrity, and it ensures the fol-
lowing.
• There are no duplicate records in a table.
• The primary key exclusively identifies each record in a table.
• Every primary key value is unique.
• Primary key values are not null.
Search WWH ::




Custom Search