title: When a query creates a new column, how do I then refer to this column in a 'Where' clause?
body: <p>My query creates a new column using a <code>CASE</code> expression.</p>
  
  <p>How do I then refer to this column in a subsequent <code>WHERE</code> clause? </p>
  
  <p>Am I best to query this column via a <code>WHEN</code> expression in the original <code>CASE</code> line?</p>