title: How to aggregate by month given start date and end date?
body: <p>I have a table <code>my_table</code> that resembles:</p>
  <pre><code>id    start_date    end_date   
  1     2019-12       2021-12
  2     2017-11       2019-03
  3     2016-09       2018-09
  </code></pre>
  <p>I have another table <code>date_values</code> with every date like:</p>
  <pre><code>date_value
  2016-09
  2016-10
  </code></pre>
  <p>I want to get the output for every month:</p>
  <pre><code>month      num_people
  2016-09    1
  2016-10    1
  </code></pre>
  <p>How would I go about doing this?</p>
  <p>I know I would need to GROUP BY month and then aggregate by COUNT(id), but I'm unsure of how to get the dates in the format I need. Would appreciate help, thanks!</p>