Yakup KALEBAŞI

Function SumLookup(ByVal items As Object()) As Decimal
    If items Is Nothing Then
        Return Nothing
    End If
 
    Dim suma As Decimal = New Decimal()
    suma = 0
    For Each item As Object In items
        suma += Convert.ToDecimal(item)
    Next
    
    Return suma
End Function

=Code.SumLookup(LookupSet(Fields!YENI_HASTA_FILTRE_DUMMY.Value,Fields!YENI_HASTA_FILTRE_DUMMY.Value,Fields!HASTA_DWID_Distinct_Count.Value, "DS_TekilHasta"))

Bkz: http://stackoverflow.com/questions/13173488/sum-two-values-from-different-datasets-using-lookups-in-report-builder

Bkz2: http://aproblemshared.fusionmanageit.co.uk/2012/08/aggregated-lookups-in-ssrs.html