title: Change column type and set not null
body: <p>How do you change the column type and also set that column to <code>not null</code> together?</p>
  
  <p>I am trying:</p>
  
  <pre><code>ALTER TABLE mytable ALTER COLUMN col TYPE character varying(15) SET NOT NULL
  </code></pre>
  
  <p>This returns an error.</p>
  
  <p>What is the right syntax?</p>