Check multiple case expressions result at once - sql

Question

I have a case expression inside an aggregate function in a select statement that looks something like this.
select person_id,
sum(case status = 'approved' then hours else 0.0 end) as hours
sum(case status = 'cancelled' then void_hrs else 0.0 end) as void_hrs
sum(case status = 'forwarded' then fwd_hrs else 0.0 end) as fwd_hrs
from table
Now, how do I check if all of the cases returns 0.0? So that I can exclude it on the result set?

Answer 1

I would just add a where clause:
select person_id,
sum(case status = 'approved' then hours else 0.0 end) as hours
sum(case status = 'cancelled' then void_hrs else 0.0 end) as void_hrs
sum(case status = 'forwarded' then fwd_hrs else 0.0 end) as fwd_hrs
from table
where status in ('approved', 'cancelled', 'forwarded')
group by person_id;
As a bonus, this might improve performance if you have a lot of rows with other statuses.
Alternatively, you can add a having clause to your query:
having sum(case when status in ('approved', 'cancelled', 'forwarded') then 1 else 0 end) > 0

Answer 2

The simplest approach is probably to turn your query to a subquery, then filter in the outer query:
select *
from (
select person_id,
sum(case status = 'approved' then hours else 0.0 end) as hours
sum(case status = 'cancelled' then void_hrs else 0.0 end) as void_hrs
sum(case status = 'forwarded' then fwd_hrs else 0.0 end) as fwd_hrs
from mytable
group by person_id
) t
where hours + void_hrs + fwd_hrs > 0
Note that your original query was missing a group by clause, I added that.
The alternative would be to use a lengthy having clause:
select person_id,
sum(case status = 'approved' then hours else 0.0 end) as hours
sum(case status = 'cancelled' then void_hrs else 0.0 end) as void_hrs
sum(case status = 'forwarded' then fwd_hrs else 0.0 end) as fwd_hrs
from mytable
group by person_id
having sum(
case status
when 'approved' then hours
when 'cancelled' then void_hrs
when 'forwarded' then fwd_hrs
else 0.0
end
) > 0
Side note: this is called a case expression, not a case statement. The latter is a flow control structure, while the former is conditional logic.