I could finally solved the problem by my self. I created a temp table which the data type for its computational fields are float like below
**CREATE TABLE #t
(
CountOfVehicle BIGINT,
LegalPersonID BIGINT,
RegionID BIGINT,
ProportionOfvehicle FLOAT,
ProportionOfAccident FLOAT,
ProportionOfPersonel FLOAT
)**
then insert into it for other fields except computational fields with code below
**INSERT INTO #t
(
CountOfVehicle,
LegalPersonID,
RegionID,
ProportionOfvehicle,
ProportionOfAccident,
ProportionOfPersonel
)
SELECT COUNT(*) AS CountOfVehicle,
LegalPersonID,
RegionID,
NULL AS ProportionOfvehicle,
NULL AS ProportionOfAccident,
NULL AS ProportionOfPersonel
FROM Bus.VehicleOwnerships
WHERE OwnershipTypeValue IN (1,2)
GROUP BY LegalPersonID,
RegionID**
and finally update the computational fields with the statement below
**UPDATE #t
SET ProportionOfvehicle = CountOfVehicle / @TotalNumberOfOrganizationVehicles
WHERE RegionID IS NOT NUL**