Group By Operator Not Behaving as Expected - sql

Question

I have this query:
SELECT groupname,
Result = CASE
WHEN ( thd_requesttype_dca_oms_form IS NULL
OR thd_requesttype_dca_oms_form = '' ) THEN
thd_requesttypeidmform
ELSE thd_requesttype_dca_oms_form
END
FROM zendeskticketexport
WHERE (groupname = 'DC Maintenance')
AND thd_requesttype_dca_oms_form = 'attribute_update_requests__discontinue___obsolete_request'
GROUP BY groupname,
thd_requesttype_dca_oms_form,
thd_requesttypeidmform
ORDER BY groupname
The result I am receiving:
groupname Result
DC Maintenance attribute_update_requests__discontinue___obsolete_request
DC Maintenance attribute_update_requests__discontinue___obsolete_request
DC Maintenance attribute_update_requests__discontinue___obsolete_request
What's throwing me off is the result; I believe the group by operator should group identical records together, but something with the group by operator in conjuction with the case operator is causing these records not to group. In testing the two cases, I see the following query is returning 0 records:
select * from ZendeskTicketExport
where groupName = 'DC Maintenance' and thd_requesttypeidmform = 'attribute_update_requests__discontinue___obsolete_request'
In my mind this would indicate that all of the records should group together, since the case operator is only returning values for the thd_requesttype_dca_oms_form field. Thanks in advance.

Answer 1

You're grouping by a third column. SQL Server will create your groups, even if that column itself isn't in the SELECT.
Try this instead:
SELECT groupname,
CASE
WHEN (thd_requesttype_dca_oms_form IS NULL OR
thd_requesttype_dca_oms_form = '' ) THEN thd_requesttypeidmform
ELSE thd_requesttype_dca_oms_form
END
FROM zendeskticketexport
WHERE
groupname = 'DC Maintenance' AND
thd_requesttype_dca_oms_form = 'attribute_update_requests__discontinue___obsolete_request'
GROUP BY groupname,
thd_requesttype_dca_oms_form,
CASE
WHEN (thd_requesttype_dca_oms_form IS NULL OR
thd_requesttype_dca_oms_form = '' ) THEN thd_requesttypeidmform
ELSE thd_requesttype_dca_oms_form
END
ORDER BY groupname