把对应表的字段跨表赋值

UPDATE MultiCompany.Finance.FwDocs

SET Quantity=aa.q,DocNo='FPDD'+ right(replicate('0',8-LEN(ID))+ltrim(ID),8)

FROM (SELECT SUM(Quantity) q,DocId dd FROM MultiCompany.Finance.FwDocDetails GROUP BY DocId) aa

WHERE Finance.FwDocs.Id=aa.dd