title: What are additional system columns defined in greenplum?
body: <p>PostgreSQL has bunch of system columns defined at <a href="http://www.postgresql.org/docs/8.3/static/ddl-system-columns.html" rel="nofollow">http://www.postgresql.org/docs/8.3/static/ddl-system-columns.html</a>.</p>
  
  <p>I am wondering what are the additional system columns defined by greenplum?</p>
  
  <p>Is there any pointer of additional description of it?</p>
  
  <p>Thanks,
  Shin</p>