[cecam]

Mirate los aggregate de un clientdataset, permiten sum, avg, count, max y min . . .

function aggregateCDS(cds:TClientDataSet; const expression:string; const valorPorDefecto:currency):currency;
var
  agg:TAggregate;
begin
  agg:=TAggregate.Create(cds.Aggregates,cds);
  agg.Expression:=expression;
  agg.Active:=True;
  if   not VarIsNull(agg.Value)
  then Result:=agg.Value
  else Result:=valorPorDefecte;
  agg.Free;
end;

Saludos!