title: Update value NULL with php in mysql
body: <p>I have this query:</p>
  
  <pre><code>UPDATE `terms` 
     SET id = '15',
         taxonomy_id = '1',
         parent_id = NULL,
         level = 0,
         position = 1,
         active = '1',
         time_created = '2012-05-24 09:31:12',
         time_updated = '0000-00-00 00:00:00' 
   WHERE id = 15
  </code></pre>
  
  <p>And I want to set the parent_id to NULL with php, but how do I do this?<br>
  These are wrong:</p>
  
  <p><code>$term-&gt;parent_id = 'NULL';</code> -> this is a string<br>
  <code>$term-&gt;parent_id = NULL;</code> -> this is empty<br>
  <code>$term-&gt;parent_id = 0;</code> -> this is an integer  </p>