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