دستور Update با join در Sql Server

update item_master
set mf_item_number = (some value)
from 
   group_master as gm
   join Manufacturar_Master as mm ON ........
where
 .... (your conditions here)

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