title: How to use MySQL index columns?
body: <p>When do you use each MySQL index type?</p>
  
  <ul>
  <li>PRIMARY - Primary key columns?</li>
  <li>UNIQUE - Foreign keys?</li>
  <li>INDEX - ??</li>
  </ul>
  
  <p>For really large tables, do indexed columns improve performance?</p>