There are a few calculation methods available in for a flowfield. This is a great feature in NAV to aggregate amounts from ledger entries. I would like Microsoft to add an option to the flowfield declaration. I would like to be able to omit zeros when using methods; Average, Exist, Count, Max and Min. In a normal SQL it is possible to use NULL to archive this result but not in NAV.
The solution that I am using now is to create a boolean field for each of the amount fields that indicate if the amount is zero. Then I have to add that boolean field to the sum-index enabled key and filter on that field.
Microsoft, please add this option to your upcoming releases of Dynamics NAV. You can vote for this here.