UPDATE VS4TPOMB Set TPOBTOExCode=(SELECT TPRMTOExCode FROM VS4TPRMB WHERE VS4TPRMB.TPRMTPRDNo=VS4TPOMB.TPOBSourceNo AND VS4TPRMB.TPRMLn=VS4TPOMB.TPOBSourceLn)
WHERE TPOBTOExCode='' or TPOBTOExCode is null
GO