SELECT
    IM1.PORT_CODE AS 港コード
  , PRT.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 PORT AS PRT
   ON IM1.PORT_CODE = PRT.PORT_CODE
INNER JOIN GRP
   ON IM1.GROUP_CODE = GRP.GROUP_CODE
INNER JOIN IMMIGRATION AS IM2
   ON IM2.KIND_CODE = '120'
  AND IM1.PORT_CODE  = IM2.PORT_CODE
  AND IM1.GROUP_CODE = IM2.GROUP_CODE
WHERE
      IM1.KIND_CODE  = '110'
  AND IM1.GROUP_CODE = '120'
  AND GRP.GROUP_NAME = '外国人'
  AND 差分 > 0
ORDER BY
  IM1.PORT_CODE DESC