title: condition in SELECT in mysql
body: <p>I have a query that looks like this</p>
  <pre><code>SELECT customer, totalvolume
  FROM orders 
  WHERE deliverydate BETWEEN '2020-01-01' AND CURDATE()
  </code></pre>
  <p>Is there any way to select totalvolume for specific date range and make it a separate column?
  So for example, I already have totalvolume. I'd like to also add totalvolume for the previous month as a separate column (totalvolume where deliverydate BETWEEN '2020-08-01' AND '2020-08-31'). Is there a function for that?</p>