select
  PORT_CODE as '港コード',
  PORT_NAME as '港名',
  SUM(case
    when KIND_CODE = 110
      then AMT
  end) as '入国者数',
  SUM(case
    when KIND_CODE = 120
      then AMT
  end) as '出国者数',
  SUM(case
    when KIND_CODE = 110
      then AMT
  end)
  - 
  SUM(case
    when KIND_CODE = 120
      then AMT
  end) as '差分'
  
from
  IMMIGRATION
--   join
--   GRP
--     using(GROUP_CODE)
  join
  PORT
    using(PORT_CODE)
where
  GROUP_CODE = 120
group by
  PORT_CODE,
  PORT_NAME
HAVING
  "差分" > 0
order by
  "差分" desc,
  PORT_CODE desc