title: Data Studio - How to get the average value within a given time frame?
body: <p>I have my connector where I'm able to get the spend value within a given time frame (on the request passed to the <code>getData</code> it has the <code>startDate</code> and <code>endDate</code> parameters and the fields with <code>spend</code>, all normal). Now I want a card that shows the average spend per day. That would be a field like</p>
  
  <pre><code>spend / DATE_DIFF(endDate, startDate)
  </code></pre>
  
  <p>But how do I pass those date values to the formula?</p>