SELECT 
    PORT.PORT_CODE
    ,PORT.PORT_NAME
    ,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 IM1.PORT_CODE = IM2.PORT_CODE
            AND IM1.GROUP_CODE = IM2.GROUP_CODE
            AND IM2.KIND_CODE = "120"
        INNER JOIN PORT
            ON IM1.PORT_CODE = PORT.PORT_CODE
WHERE
    IM1.KIND_CODE = "110"
    AND IM1.GROUP_CODE = "120"
    AND (IM1.AMT - IM2.AMT) > 0
ORDER BY
    差分 DESC
    ,PORT.PORT_CODE DESC