title: Finding pairs that do not exist in a different table
body: <p>I have a table (orders) with order id, location 1, location 2 and another table (mileage) with location 1 and location 2.</p>
  
  <p>I'm using the Except action to return those location pairs in orders that are not in mileage. But I'm not sure how I can also return the corresponding order_id that belongs to those pairs (order_id doesn't exist in the mileage table). The only thing I can think of is having an outer select statement that searches orders for those location pairs. I haven't tried it but I'm looking for other options.</p>
  
  <p>I have something like this.</p>
  
  <pre><code>SELECT location_id1, location_id2  
  FROM orders 
  except
  SELECT lm.origin_id, lm.dest_id
  from mileage
  </code></pre>
  
  <p>How can I also retrieve the order id for those pairs?</p>