Sum(distin​ct) equivalent question

[ivank]

I have a table, There is a primarykey InvoiceID, there is a secondaryprimarykey ProductID and there is a field TotalProduct. I want the sum(distinct field totalproduct) for a particular value of InvoiceID. Without the distinct function I arrive at multiple values in various rows of the portal readout - equivalent to simply Sum( field totalproduct)

How do I get the Distinct effect in Filemaker?
 

[comment]

I don't understand your description. Can you provide a real-life example where this is necessary?