SELECT
    IM1.PORT_CODE AS 港コード
    , PT.PORT_NAME AS 港名
    , 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 IM2.port_code = IM1.port_code
        and IM2.group_code = IM1.group_code
        and IM2.kind_code = "120"
    inner join port as PT
        on PT.port_code = im1.port_code
where
    IM1.group_code = "120"
    and IM1.kind_code = "110"
    and 差分 > 0
ORDER BY
    差分 DESC
    , IM1.PORT_CODE DESC;