select
   s.port_code  as '港コード'
  ,pt.port_name as '港名'
  ,s.kind_code_im as '入国者数'
  ,s.kind_code_ex as '出国者数'
  ,s.kind_code_im - s.kind_code_ex as '差分'
from (
  select
     t.port_code
    ,sum(case t.kind_code when '110' then t.amt else 0 end) as kind_code_im
    ,sum(case t.kind_code when '120' then t.amt else 0 end) as kind_code_ex
  from immigration as t
  inner join grp as gp
  on t.group_code = gp.group_code
  where gp.group_name = '外国人'
  group by 
     t.port_code
) AS s
left outer join port as pt
on s.port_code = pt.port_code
where
  s.kind_code_im > s.kind_code_ex
order by
   差分 DESC
  ,港コード DESC