SELECT
    IMMIGRATION.PORT_CODE AS 港コード,
    PORT.PORT_NAME AS 港名,
    SUM(CASE 
        WHEN KIND_CODE = 110
            THEN AMT
    END )AS 入国者数,
    SUM(CASE
        WHEN KIND_CODE = 120
            THEN AMT
    END) AS 出国者数,
    SUM(CASE 
        WHEN KIND_CODE = 110
            THEN AMT
    END)
    - 
    SUM(CASE
        WHEN KIND_CODE = 120
            THEN AMT
    END) AS 差分
FROM
    IMMIGRATION
    INNER JOIN
        GRP
        ON
        IMMIGRATION.GROUP_CODE = GRP.GROUP_CODE
    INNER JOIN
        PORT
        ON
        IMMIGRATION.PORT_CODE = PORT.PORT_CODE
WHERE
    IMMIGRATION.GROUP_CODE = 120
GROUP BY
    IMMIGRATION.PORT_CODE
HAVING
    差分 > 0
ORDER BY
    差分 DESC,
    IMMIGRATION.PORT_CODE DESC