title: how to select every month even they do not have value
body: <p>I want to select company id, date and number from table, but this query does not show the month some companies with 0 number. </p>
  
  <p>Here is the query:</p>
  
  <pre><code>SELECT c.name, date_format(e.created, '%y_%m') AS date, count(*) 
  FROM company c
  JOIN edited e
  on c.id=e.company_id AND e.created &gt;='2016-12-13 00:00:00' AND e.created &lt;='2017-05-20 00:00:00'
  GROUP BY c.id, date
  </code></pre>
  
  <p>Some of results like this  4   16_12    2
          4   17_01   4
          4   17_04   2
          4   17_05   2
  without 17_03 (march). how can it show 17_03 with 0 ?</p>