Hi Peter Eschweg...
Can You explain clear what you mean by double dates...
SELECT T0.[Cardcode], T0.[CardName], T0.[DocNum], T0.[GroupNum], Max(T0.[TaxDate])
FROM ORDR t
join ( select Fax from OCRD T1 group by T1.[Fax]) i
ON T0.CardCode = T1.CardCode
WHERE (T0.[TaxDate] >= CAST(MONTH(DATEADD(m, - 4, GETDATE())) AS varchar) + '.1. ' + CAST(YEAR(DATEADD(m, - 4, GETDATE())) AS varchar))
Group by T0.[Cardcode], T0.[CardName], T0.[DocNum]
Try This
Regards
Kennedy