title: Filling NULL value again on deletion or updation
body: <p>I have updated certain field in my database &amp; that field has default value as NULL. How can I again fill NULL if field is emptied or deleted. As during this updation blank value is filled in database and of course that is not NULL. Is filling NULL instead  of blank value good? </p>
  
  <p>Using php how can I do that? Suppose I have condition if code</p>
  
  <pre><code>if(!empty($photo))
  { $a in database;
  }
  </code></pre>
  
  <p>But in this condition if <code>$photo</code> is empty it will fill blank value of <code>$a</code>... Let me know to fill NULL in database.</p>