title: MySQL EXPLAIN EXTENDED filtered column (obviously it's not a percentage)
body: <p>I've been searching for this and they all state some sort of percentage, explain this:</p>
  
  <pre><code>EXPLAIN EXTENDED SELECT * FROM PageAccess ORDER BY AccessId DESC LIMIT 20;
  SELECT COUNT(*) FROM PageAccess;
  </code></pre>
  
  <p>Giving:</p>
  
  <pre><code>id, select_type, table, type, possible_keys, key, key_len, ref, rows, filtered, Extra
  1, 'SIMPLE', 'PageAccess', 'index', '', 'PRIMARY', '4', '', 20, 9295.00, ''
  </code></pre>
  
  <p>(Yes, filtered = 9295.00)</p>
  
  <p>and:</p>
  
  <pre><code>1830
  </code></pre>
  
  <p>For count(*)</p>
  
  <p>Yes I want the last 20 rows, AccessId is the auto-incremented primary key.</p>
  
  <p>What does 9295 mean!?</p>