SELECT
    IM.PORT_CODE AS 港コード
    , PO.PORT_NAME AS 港名
    , IM.AMT AS 入国者数
    , IM2.AMT AS 出国者数
    , (IM.AMT - IM2.AMT) AS 差分 

FROM
    IMMIGRATION as IM
    inner join PORT as PO
    on IM.PORT_CODE = PO.PORT_CODE
    inner join GRP as GR
    on IM.GROUP_CODE = GR.GROUP_CODE
    inner join IMMIGRATION as IM2
    on IM.PORT_CODE = IM2.PORT_CODE
    AND IM2.GROUP_CODE = IM.GROUP_CODE
    AND IM2.KIND_CODE = '120'
    
WHERE
    IM.GROUP_CODE = '120'
    AND IM.KIND_CODE = '110' 
    AND 差分 > 0 
ORDER BY
    差分 DESC
    , IM.PORT_CODE DESC;