title: What does it mean by the value under 'filtered' column in EXPLAIN EXTENDED of a Mysql SELECT
body: <p>what does it mean to us when the filtered column in EXPLAIN EXTENDED shows 100%.</p>
  
  <p>What is the difference between the below two situations...?</p>
  
  <ol>
  <li>filtered = 100% in query 1 for column X</li>
  <li>filtered = 10% in query 2 for column Y</li>
  </ol>
  
  <p>What is the optimal value for filtered column in EXPLAIN EXTENDED....?</p>
  
  <p>Thanks in advance</p>