SELECT tblDoc.SSkl, tblStavke.NSN, tblDoc.DatDPos, Sum([klc]*[VriP]) AS Kolicina
FROM tblVrDoc INNER JOIN (tblDoc INNER JOIN tblStavke ON tblDoc.BrD = tblStavke.BrD) ON tblVrDoc.VrDoc = tblDoc.VrDoc
GROUP BY tblDoc.SSkl, tblStavke.NSN, tblDoc.DatDPos
ORDER BY tblStavke.NSN, tblDoc.DatDPos;