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