Question

I have the following SQL problem.

Scenario:

I have two tables: Change and ChangeTicket.
There is a 1:n relationship. One Change has cero or many changeTickets.
No change means no changeTickets.
A changeTicket has a status (open/closed/…)
A changeTicket has a field representing how many minutes took this change.

A Change has a company and a month. There is at most ONE change in the month.

I have to report for a given company and for a given month the sum of minutes
a given change took.

I wrote the following SQL statement.

select  nvl(sum(service_req), 0) as SUM_REQ 
from Change_Ticket, Change
where Change.company_id (+) = '0' 
  and Change.month (+)='07'
  and Change.Id  (+) = Change_Ticket.Change_Id 

This is OK.

If for the given month and the given company there are neither changes nor tickets
then I get a null value which is converted to cero usgin the NVL function.

The problem arises when I want to group the information using the status.
If I add a grup clause

select  Change_Ticket.status, nvl(sum(service_req), 0) as SUM_REQ 
from Change_Ticket, Change
where Change.company_id (+) = '0' 
  and Change.month (+)='07'
  and Change.Id  (+) = Change_Ticket.Change_Id 
group by Change_Ticket.status

then my result is the empty set.
I understand that there is no status and then the resulting set is
somehow consistent and then an empty resulting set is returned.

How can I avoid this problem. In this case I need to report an
empty status and cero as the the sum.

(BTW, I’ve also tried putting nvl(Change_Ticket.status, ‘none’) but didn’t work)

Thanks a lot in advance.

Luis

Answer 1

I think to achieve what you want you would need to do this:

select  Change_Ticket.status, nvl(sum(service_req), 0) as SUM_REQ 
from Change_Ticket, Change
where Change.company_id (+) = '0' 
  and Change.month (+)='07'
  and Change.Id  (+) = Change_Ticket.Change_Id 
group by Change_Ticket.status
union all
select '' as STATUS, 0 as SUM_REQ
from dual
where not exists (select null from Change_ticket)