ORACLE, SQL SERVER - typical update with subselect

update factory.an_plan a
set
a.sbj_id = ( select sbj_id from j_vad
             where
        vad_id = ( select vad_id from kuauko
                 where
            bsg_nr = a.bsg_nr
        )
    )
where
a.c_period = pPeriod and
a.bsg_nr is not null;