title: Sorting a VARCHAR column as FLOAT using the CAST operator don't work in MySQL
body: <p>I can't find a way to sort a varchar column casted as float. Here is my SQL request:</p>
  
  <pre><code>SELECT guid, number FROM table ORDER BY 'CAST(number AS FLOAT) DESC'
  </code></pre>
  
  <p>The "number" column is defined like this:</p>
  
  <pre><code>number  varchar(20) ascii_general_ci
  </code></pre>
  
  <p>And the values defined in this column for my test are :</p>
  
  <pre><code>0.00
  200.00
  20.00
  100.00
  </code></pre>
  
  <p>MySQL totally ignore the CAST operator and sort the columns by guid...</p>
  
  <p>Is there a bug in MySQL or did I do something wrong ?</p>