Google "filemaker summary field"
Are these your relationship?
Consumers::ConsumerID = Invoices::ConsumerID
Consumers::ConsumerID = InvoicesByMonth::ConsumerID AND
Consumers::Month = InvoicesByMonth::Month
InvoicesByMonth being a second occurrence of Invoices.
If so, you can get the totals for a given consumer and month by using:
Sum ( InvoicesByMonth::InvoiceAmount ) // Use your field from Invoices that computes the invoice total
or you can use a summary field as recommended by davidanders. If you define a field, sInvoiceTotal, in Invoices as a summary field that computes the total of your InvoiceAmount, you can place InvoiceByMonth::sInvoiceTotal on your consumers layout to display a monthly total.
PS. If I were to use "Month" fields as shown above, consumers::Month would be a global date field with an auto-enter calculation: Self - Day ( Self ) + 1 to convert any date entered into it into the date of the first day of the same month. And InvoicesByMonth::MOnth would be a calculation field defined as: Invoicedate - Month ( InvoiceDate ) + 1 to return the date of the first day of the same month as InvoiceDate.
And in FileMaker 11, you do not need the second relationship in many cases, a filtered one row portal to Invoices on the Consumers layout can display sInvoiceTotal with a filter that filters out all related invoices save those of a specified month and year.
I really don't get it. The thing that I don't understand is if the relation says this phrase: İf the months are the same and the consumer id is the same sum all of them. Why it doesn't do it?
The method I described does exactly that. Why it doesn't do that for you, is not a question I can answer without a more detailed description of what you have set up and how it isn't working.
I just realised my mistake. Thank you very much for your help and sorry for the trouble.