Question

In the example table below, I’m trying to figure out a way to sum amount over id for all marks where mark ‘C’ doesn’t exist within an id. When mark ‘C’ does exist in an id, I want the sum of amounts over that id, excluding the amount against mark ‘A’. As illustration, my desired output is at the bottom. I’ve considered using partitions and the EXISTS command, but I’m having trouble conceptualizing the solution. If any of you could take a look and point me in the right direction, it would be greatly appreciated 🙂

sample table:

id   mark  amount
------------------
1    A     1
2    A     3
2    B     2
3    A     2
4    A     1
4    B     3
5    A     1
5    C     3
6    A     2
6    C     2

desired output:

id   sum(amount)
-----------------
1    1
2    5
3    2
4    4
5    3
6    2

Answer 1

select 
  id, 
  case 
     when count(case mark when 'C' then 1 else null end) = 0 
     then 
        sum(amount)
     else 
        sum(case when mark <> 'A' then amount else 0 end)
  end
from sampletable
group by id