title: Redshift convert dates to unix timestamps
body: <p>I have a column of dates in a Redshift table. I would like the output to be in the form of unix timestamps.
  Essentially, I want the opposite of this question: <a href="https://stackoverflow.com/questions/39815425/how-to-convert-epoch-to-datetime-redshift">How to convert epoch to datetime redshift?</a></p>
  
  <p>Is there a way to do this?</p>