Hi,
Try this query:
SELECT T0.[DocNum],sum(T3.[LineTotal]) FROM ORDR T0 INNER JOIN RDR1 T1 ON T0.DocEntry = T1.DocEntry left join OPOR T2 on T2.[DocNum] = T1.[PoTrgNum] INNER JOIN POR1 T3 ON T2.DocEntry = T3.DocEntry GROUP BY T0.[DocNum]
Thanks & Regards,
Nagarajan