title: Count of number of unique customers by month
body: <p>I have a spreadsheet that contains data for customers that have purchased items from my store.  What I would like to do is go back the last couple years, using a pivot table, and display: number of customers that ordered something each month (a count of unique customer names).</p>
  <p>The sheet is organized as such:</p>
  <pre><code>Date     | Invoice | Account Name     | Item            | Quantity | Amount
  6/1/2020 | 50100   | John's Tire Shop | 1/2 Inch Socket | 2        | 12.00
  </code></pre>
  <p>Is there a way inside pivot table options to count unique account names and display the total grouped by month?</p>