SELECT
    PO.PORT_CODE  AS 港コード
    , PO.PORT_NAME AS 港名
    , IM1.AMT AS 入国者数
    , IM2.AMT AS 出国者数
    , CAST(IM1.AMT AS REAL) - CAST(IM2.AMT AS REAL) AS 差分
FROM
    PORT AS PO 
    INNER JOIN IMMIGRATION AS IM1
        ON PO.PORT_CODE = IM1.PORT_CODE
        AND IM1.KIND_CODE = 110
    INNER JOIN IMMIGRATION AS IM2
        ON PO.PORT_CODE = IM2.PORT_CODE
        AND IM2.KIND_CODE = 120
WHERE
    IM1.GROUP_CODE = 120 
    AND 差分 > 0
ORDER BY
    差分 DESC
    , 港コード DESC;