select c.cname
from   customers c
where  not exists (select e.eno
                   from   employees e, zipcodes z
                   where  z.city = 'Wichita' and
                          e.zip = z.zip and not 1020 in 
                          (select x.ono
                          from   orders x       
                          where  x.ono = 1020));

