title: What is the difference between primary, unique and foreign key constraints, and indexes?
body: <p>What is the difference between <code>primary</code>, <code>unique</code> and <code>foreign key constraints</code>, and <code>indexes</code>? </p>
  
  <p>I work on <code>Oracle 10g</code> and <code>SQL Server 2008</code></p>