title: SQL cannot identify datatype SERIAL
body: <p>Thanks in advance,<br>
  I do not get why SERIAL is not recognized as a data type.<br>
  the code is really simple tho.<br>
  I also have a question:
  Since SERIAL is not a true type, do I have to define it somewhere?</p>
  <pre><code>CREATE TABLE flights (
      id SERIAL PRIMARY KEY,
      origin VARCHAR NOT NULL,
      destination VARCHAR NOT NULL,
      duration INTEGER NOT NULL,
  );
  </code></pre>
  <p><a href="https://i.stack.imgur.com/12cit.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/12cit.png" alt="enter image description here" /></a></p>