Sum of same field in multiple datasources

Hi,

I would like to ask if it is possible to acquire the sum of the same field, in the same table, but from multiple datasources.

I know that

=NL("Sum","Table","Field","datasource=","Datasource1")+NL("Sum","Table","Field","datasource=","Datasource2")+NL("Sum","Table","Field","datasource=","Datasource3")

or displaying each value on the same row and summing it up will work, but the issue is that I have about 40+ datasources to do so (don't ask why ;/). Hence, is there an alternate method?