Database Design for Mere Mortals™: A Hands-On Guide to Relational Database Design, Second Edition

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.

• Its value is not optional in whole or in part.

• It comprises a minimum number of fields necessary to define uniqueness.

• Its values must uniquely and exclusively identify each record in the table.

• Its value must exclusively identify the value of each field within a given record.

• Its value can be modified only in rare or extreme cases.

Rules for Establishing a Primary Key

• Each table must have one—and only one—primary key.

• Each primary key within the database must be unique—no two tables should have the same primary key unless ...