title: Redshift: add column if not exists
body: <p>The following <a href="https://stackoverflow.com/a/38721951/1291563">works in Postgres 9.6</a> but not in Redshift:</p>
  
  <pre><code>ALTER TABLE stats
      ADD COLUMN IF NOT EXISTS panel_exit timestamp;
  </code></pre>
  
  <p>Can the same functionality be achieved in Redshift?</p>