Otherwise, please give some more details. Perhaps post the SQL of your
query, the data on which it runs, the results it gives, and what you want it
to produce.
If you use Nz( A + B,0) and either of those is null, then you will get 0
regardless of the value of the other. For example:
A= 50 and B = Null
The results will be Null, because the addition happens prior to the Nz
function. It has to be like this:
Nz(A,0) + Nz(B,0)
Now it will return 50
B was converted to 0 and 50 + 0 = 50