Update a table with results from multiple tables - sql-server-2012

Question

Currently using Microsoft SQL Server 2012 (Management Studio), looking to update a column in a table with a query which uses data from another table.
This is the query I am running:
SELECT
tblGeneralVehicleInformation.EngineerVehicleReg, tblModel.Model_ID,
tblModel.VanOrCar, tblModel.Model, tblMake.Make_ID,
tblMake.WarrantyCars, tblMake.WarrantyVans,
tblMake.WarrantyCarMonths, tblMake.WarrantyVanMonths,
tblGeneralVehicleInformation.PurchaseDate,
tblGeneralVehicleInformation.Mileage
FROM
tblGeneralVehicleInformation
INNER JOIN
tblModel ON tblGeneralVehicleInformation.Model_IDFK = tblModel.Model_ID
INNER JOIN
tblMake ON tblGeneralVehicleInformation.Make_IDFK = tblMake.Make_ID
UPDATE dbo.tblGeneralVehicleInformation
SET WarrantyId = '1'
WHERE (tblModel.VanOrCar = N'Van')
AND (Mileage > WarrantyVans)
AND (DateDiff("M",PurchaseDate,CURRENT_TIMESTAMP) > WarrantyVanMonths)
Should this work or are you not able to have a query like the above within the UPDATE statement?
Thanks for your help

Answer 1

You need to combine both into a single statement. I would also advise you start using table aliases to make your code a little more readable...
UPDATE v
SET WarrantyId = '1'
FROM tblGeneralVehicleInformation v
INNER JOIN tblModel mo
ON v.Model_IDFK = mo.Model_ID
INNER JOIN tblMake ma
ON v.Make_IDFK = ma.Make_ID
WHERE (mo.VanOrCar = N'Van')
AND (Mileage > WarrantyVans)
AND (DateDiff("M",PurchaseDate,CURRENT_TIMESTAMP) > WarrantyVanMonths)