SELECT
    PORT_CODE,
    PORT_NAME,
    AMT_1,
    AMT_2,
    AMT_1 - AMT_2
FROM
    PORT
INNER JOIN (
    SELECT
        PORT_CODE,
        AMT AS AMT_1
    FROM
        PORT
    INNER JOIN
        IMMIGRATION USING (PORT_CODE)
    INNER JOIN
        GRP USING (GROUP_CODE)
    WHERE
        GROUP_CODE = 120
        AND KIND_CODE = 110
) USING (PORT_CODE)
INNER JOIN (
    SELECT
        PORT_CODE,
        AMT AS AMT_2
    FROM
        PORT
    INNER JOIN
        IMMIGRATION USING (PORT_CODE)
    INNER JOIN
        GRP USING (GROUP_CODE)
    WHERE
        GROUP_CODE = 120
        AND KIND_CODE = 120
) USING (PORT_CODE)
ORDER BY
    AMT_1 - AMT_2 DESC,
    PORT_CODE DESC