title: Mysql query WHERE clause not working. WHERE useDate<>CURDATE()
body: <p><code>useDate</code> is date type and is <code>NULL</code>.
  The query below doesn't work</p>
  
  <pre><code>UPDATE licenses 
       SET useDate = CURDATE() 
  WHERE license = 'ABC123' AND useDate &lt;&gt; CURDATE();
  </code></pre>