title: Are there any reason to use both primary key and unique key together on the same field?
body: <p>I am analyzing an Oracle database design and I am perplexed at seeing both unique keys and primary keys on the same fields. These unique-primary key pairs are consistently created on all tables. I see no reason to do this. </p>
  
  <p>If I have a primary key anyway, is there a good reason to create an additional unique key on the same field?</p>