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select room.* , isnull(guest.guestname , '') guestname
from room
left join booking on room.roomno = gooking.roomno
left join guest on booking.guestno = guest.guestno
select a.*,isnull(guestname,'')guestname from room a
left join booking c on a.roomno=c.roomno
left join guest b on b.guestno=c.guestno