title: IN Clause with NULL or IS NULL
body: <p>Postgres is the database</p>
  
  <p>Can I use a NULL value for a IN clause? example:</p>
  
  <pre><code>SELECT *
  FROM tbl_name
  WHERE id_field IN ('value1', 'value2', 'value3', NULL)
  </code></pre>
  
  <p>I want to limit to these four values.</p>
  
  <p>I have tried the above statement and it doesn't work, well it executes but doesn't add the records with NULL id_fields.</p>
  
  <p>I have also tried to add a OR condition but this just make the query run and run with no end in sight.</p>
  
  <pre><code>SELECT *
  FROM tbl_name
  WHERE other_condition = bar
  AND another_condition = foo
  AND id_field IN ('value1', 'value2', 'value3')
  OR id_field IS NULL
  </code></pre>
  
  <p>Any suggestions? </p>