title: MySQL's Group_Concat function miss the nulls. How can group the rows including NULLs.
body: <p>Consider the following example of Table1 <p></p>
  
  <pre><code>usrID orderID deliverID
  1     303     102
  1     304     103
  2     305     NULL
  2     306     105
  3     307     NULL
  3     308     NULL
  </code></pre>
  
  <p>I want to concat the orderID, deliverID and group as usrID, as following<p></p>
  
  <pre><code>usrID orderID_group deliverID_group
  1     303,304       102,103
  2     305,306       NULL,105
  3     307,308       NULL,NULL
  </code></pre>
  
  <p>I am using the following MySQL query which miss the NULL value. <p></p>
  
  <pre><code>SELECT usrID,
         GROUP_CONCAT(orderID SEPARATOR “,” ) AS orderID_group,
         GROUP_CONCAT(deliverID SEPARATOR “,”) AS deliverID_group
  FROM   table1
  GROUP  BY usrID;
  </code></pre>
  
  <p>I want to include both NOT NULL and NULL in sequence order. I would appreciate if anyone kindly write the MySQL query. Thanks</p>