title: I need to auto_increment a field in MySQL that is not primary key
body: <p>Right now, I have a table whose primary key is an <code>auto_increment</code> field. However, I need to set the primary key as <code>username</code>, <code>date</code> (to ensure that there cannot be a duplicate username with a date).</p>
  
  <p>I need the <code>auto_increment</code> field, however, in order to make changes to row information (adding and deleting).</p>
  
  <p>What is normally done with this situation?</p>
  
  <p>Thanks!</p>