Calculated Value with pre-aggregation

[Giuseppe Verardi]

Good morning,

I need to create following query with a Calculated Value:

select avg(result)

from (

select abs(sum(A) - sum(B))/sum(A) as result

from Table

group by C) as t

There is a pre-aggregation for A and B, I don't be able to make avg(result) in a Calculated Value, how can I do