select
  p.PORT_CODE as 港コード
  ,p.PORT_NAME as 港名
  ,IFNULL(i110.AMT,0) as 入国者数
  ,IFNULL(i120.AMT,0) as 出国者数
  ,IFNULL(i110.AMT,0) - IFNULL(i120.AMT,0) as 差分
from PORT p
  inner join IMMIGRATION i110
    on p.PORT_CODE = i110.PORT_CODE
    and i110.GROUP_CODE = '120'
    and i110.KIND_CODE = '110'
  inner join IMMIGRATION i120
    on p.PORT_CODE = i120.PORT_CODE
    and i120.GROUP_CODE = '120'
    and i120.KIND_CODE = '120'
where
  IFNULL(i110.AMT,0) - IFNULL(i120.AMT,0) > 0
order by
  IFNULL(i110.AMT,0) - IFNULL(i120.AMT,0) desc
  ,p.PORT_CODE desc