How can I get a non empty result set when using select, group by and count?

Question

This is the current query:

SELECT status.ct_reconcile_status, 
       IFNULL(COUNT(status.ct_reconcile_status), 0) AS sch_change_status_num 
FROM   db_crewops_cm_action status 
WHERE  status.ct_reconcile_status IN ( 'SUCCESS', 'FAILED' ) 
       AND status.updated_ts > UTC_TIMESTAMP() - INTERVAL 60 minute 
GROUP  BY status.ct_reconcile_status; 

And the result I want to get looks like this:

SUCCESS   5
FAILED    9

and that's ok. The problem is that I could get a case where the number of results is 0 for both statuses and in that case I want this:

SUCCESS   0
FAILED    0

and not an empty results set (what I get now). I have a general idea that I should either join the table on itself or use a WITH clause but I have no idea how to start that.

Answer 1

Try something like:

SELECT a.status AS ct_reconcile_status,
       (IFNULL(b.sch_change_status_num,0) + a.num) AS sch_change_status_num
FROM
  (SELECT 'SUCCESS' AS status, 0 AS num
   UNION
   SELECT 'FAILED', 0) a
LEFT JOIN
  (SELECT status.ct_reconcile_status, 
          COUNT(status.ct_reconcile_status) AS sch_change_status_num 
   FROM   db_crewops_cm_action status 
   WHERE  status.ct_reconcile_status IN ( 'SUCCESS', 'FAILED' ) 
          AND status.updated_ts > UTC_TIMESTAMP() - INTERVAL 60 minute 
   GROUP  BY status.ct_reconcile_status) b
ON a.status = b.ct_reconcile_status

You can remove status.ct_reconcile_status IN ( 'SUCCESS', 'FAILED' ) AND, but this could be slower.