SELECT
  IM1.PORT_CODE as '港コード',
  PT.PORT_NAME as '港名',
  IM1.AMT as '入国者数',
  IM2.AMT as '出国者数',
  (IM1.AMT - IM2.AMT) as '差分'
FROM
  IMMIGRATION as IM1
  INNER JOIN IMMIGRATION as IM2
    ON IM2.PORT_CODE = IM1.PORT_CODE
    AND IM2.GROUP_CODE = IM1.GROUP_CODE
    AND IM2.KIND_CODE = '120'
  INNER JOIN PORT as PT
    ON PT.PORT_CODE = IM1.PORT_CODE
WHERE
  IM1.GROUP_CODE = '120'
  AND IM1.KIND_CODE = '110'
  AND 差分 > 0
ORDER BY
  '差分' DESC,
  IM1.PORT_CODE DESC;