title: What does regclass mean in Postgresql
body: <p>I have the following line in a CREATE TABLE statement:</p>
  <pre><code>field1_id bigint DEFAULT nextval('table1_field1_id_seq'::regclass) NOT NULL,
  </code></pre>
  <p>What does regclass mean in the above? Is it an absolute requirement to add <code>::regclass</code>?</p>
  <p><strong>N.B:</strong> I had seen the Postgresql documentation <a href="http://www.postgresql.org/docs/current/static/datatype-oid.html" rel="noreferrer">link</a> which tells about <code>regclass</code>, but couldn't understand it.</p>