use T25s001

UPDATE ACCOUNT_MASTER SET UdyamRegNumber=T1.UdyamRegNumber,EnterpriseType=T1.EnterpriseType,EnterpriseActivity=T1.EnterpriseActivity 
FROM (SELECT AccCode As AccCd, AccName, AccAgentCode, AccGroupCode, AccAdd1, AccAdd2, AccAdd3, AccCityName, AccCityPin, AccPhone, AccMobile, AccFax, AccEmail, AccResident, AccGSTNo, AccCSTNo, AccPANNo, AccVATNo, AccContPerson, AccRef, AccCrLimit, AccCrDays, AccTANNo, AccKSTNo, TDSYesNo, TDSAccount, DiscPerc, RDPerPcs, RDPerMts, JobType, InsPolicyNo, Taxable, GSTIN, CompScheme, GSTCategory, GSTRegDate, AccManager, CityDistanceKM, TransName, BlackListed, UdyamRegNumber, EnterpriseType, EnterpriseActivity 
FROM T24s001.dbo.ACCOUNT_MASTER) AS T1 WHERE T1.AccCd COLLATE DATABASE_DEFAULT= AccCode and ACCOUNT_MASTER.UdyamRegNumber=''