title: Select from column including null values
body: <p>I'm trying to create <code>SELECT</code> that includes various foreign key to list all the rows it has, but there is two foreign key that can be null.</p>
  
  <p><code>bank_id</code> and <code>bbank_id</code> can be null, so with this example it only will list rows that doesn't have null values in <code>bank_id</code> and <code>bbank_id</code>, but I need it to return rows where <code>bank_id</code> and <code>bbank_id</code> are null or not null. 
  I tried using <code>IS NOT NULL AND NULL</code>, well it doesn't work.</p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT E.emp_id, E.emp_name, E.emp_surname1, E.emp_surname2,  
  J.job_name, U.ubi_name, D.dep_name, POR.por_type, 
  B.bank_name, BB.bbank_name
  FROM public.employee E, public.ubi U, 
  public.jobs J, public.department D, 
  public.percenttable POR, public.bank B, 
  public.bbank BB
  WHERE E.ubi_id = U.ubi_id AND E.job_id = J.job_id
  AND E.dep_id = D.dep_id AND E.por_id = POR.por_id
  AND E.bank_id = B.bank_id AND E.bbank_id = BB.bbank_id
  AND E.ubi_id IS NOT NULL AND E.job_id IS NOT NULL AND E.dep_id IS NOT NULL
  AND E.por_id IS NOT NULL AND E.bank_id IS NOT NULL AND E.bbank_id IS NOT NULL
  ORDER BY E.emp_id ASC;
  </code></pre>
  
  <p>I read something about using LEFT JOIN but no idea how to implement it here.</p>