title: What's the difference between composite primary index and two primary indexes?
body: <p>I'm using phpmyadmin and have discovered that you can only have one <code>PRIMARY</code> key/index (if they're interchangeable in that context) for a table, but it can contain multiple columns. </p>
  
  <p>If you can have such, why does it not allow the creation of more than one <code>PRIMARY</code> key/index?</p>