title: Add new column with foreign key constraint in one command
body: <p>I am trying to add a new column that will be a foreign key. I have been able to add the column and the foreign key constraint using two separate <code>ALTER TABLE</code> commands:</p>
  
  <pre><code>ALTER TABLE one
  ADD two_id integer;
  
  ALTER TABLE one
  ADD FOREIGN KEY (two_id) REFERENCES two(id);
  </code></pre>
  
  <p>Is there a way to do this with one ALTER TABLE command instead of two? I could not come up with anything that works. </p>