title: mysql datetime comparison
body: <p>For example the following query works fine:</p>
  
  <pre><code>SELECT * 
    FROM quotes 
   WHERE expires_at &lt;= '2010-10-15 10:00:00';
  </code></pre>
  
  <p>But this is obviously performing a 'string' comparison - I was wondering if there was a function built in to MySQL that specifically does 'datetime' comparisons.</p>