title: How to select rows having column value as null?
body: <p>Consider following database table:  </p>
  
  <pre><code>id      |  is_visible
  ________|_______________
  1       |  true
  2       |  false
  3       |               -- i.e. null
  </code></pre>
  
  <p>I want to select all the rows having is_visible = null. I tried the following queries:</p>
  
  <pre><code>SELECT * FROM tab WHERE is_visible = null;     -- 0 results
  SELECT * FROM tab WHERE is_visible &lt;&gt; true;    -- only fields with false value
  SELECT * FROM tab WHERE is_visible &lt;&gt; false;   -- only fields with true
  </code></pre>
  
  <p>I tried it in postgresql and sql server<br>
  How to select rows having is_visible = null?</p>