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