title: Nested loops in MySQL
body: <p>In <a href="http://assets.en.oreilly.com/1/event/2/EXPLAIN%20Demystified%20Presentation.pdf" rel="noreferrer">this O'Reilly presentation</a>, there is a paragraph introducing some key concepts for understanding MySQL's EXPLAIN:</p>
  
  <blockquote>
    <p>What is a JOIN?</p>
    
    <ul>
    <li>Everything is a JOIN, because MySQL always uses nested-loops </li>
    <li>Even a single-table SELECT or a UNION or a subquery</li>
    </ul>
  </blockquote>
  
  <p>Can anyone explain how this works for a single table SELECT?</p>