sql server - SQL update query using joins

I have to update a field with a value which is returned by a join of 3 tables.

Example:

select
    im.itemid
    ,im.sku as iSku
    ,gm.SKU as GSKU
    ,mm.ManufacturerId as ManuId

    ,mm.ManufacturerName
    ,im.mf_item_number
    ,mm.ManufacturerID
from 
    item_master im, group_master gm, Manufacturer_Master mm 
where
    im.mf_item_number like 'STA%'
    and im.sku=gm.sku
    and gm.ManufacturerID = mm.ManufacturerID
    and gm.manufacturerID=34

I want to update the mf_item_number field values of table item_master with some other value which is joined in the above condition.

How can I do this in MS SQL Server?

Answer

UPDATE im
SET mf_item_number = gm.SKU --etc
FROM item_master im
JOIN group_master gm

    ON im.sku = gm.sku 
JOIN Manufacturer_Master mm
    ON gm.ManufacturerID = mm.ManufacturerID
WHERE im.mf_item_number like 'STA%' AND
      gm.manufacturerID = 34

To make it clear... The UPDATE clause can refer to an table alias specified in the FROM clause. So im in this case is valid

Generic example

UPDATE A
SET foo = B.bar
FROM TableA A
JOIN TableB B
    ON A.col1 = B.colx
WHERE ...