title: Difference between "IS NOT NULL" and "NOT (field = NULL)" in these 2 queries
body: <p>What is the difference between the following 2 queries?</p>
  
  <pre><code>DELETE FROM experience WHERE end IS NOT NULL;
  </code></pre>
  
  <p>And</p>
  
  <pre><code>DELETE FROM experience WHERE NOT( end=NULL);
  </code></pre>
  
  <p>First query was accepted as a correct answer but second was not.</p>