Eventuell so? (Ungetestet)
Code:
update sys.zst_2bmobil mo
set mo.angeliefert = '1'
where Cast(mo.AUFTRAG_ID as Varchar(20))+'-'+Cast(mo.ZAEHLERNUMMER as Varchar(20))+'-'+ cast(mo.ZAEHLWERKNUMMER as Varchar(20)) IN
( Select Cast(m.AUFTRAG_ID as Varchar(20))+'-'+Cast(m.ZAEHLERNUMMER as Varchar(20))+'-'+ cast(m.ZAEHLWERKNUMMER as Varchar(20))
from sys.zst_2bmobil m
left join sys.zst_lager l
on m.zaehlernummer = l.geraet
where m.zaehleraltneu=1
and m.angeliefert is null
and m.ablesedatum >= '27.07.2016'
and m.ort <> 'Dorsten'
and l.datum_bis = '31.12.9999'
and l.lagertyp = '302')