SELECT
      港コード
	, 港名
    , 入国者数
    , 出国者数
    , 差分
FROM
   (
    select
         IMMIGRATION.PORT_CODE AS '港コード'
        ,PORT.PORT_NAME AS '港名'
        ,SUM(CASE WHEN KIND_CODE = '110' THEN AMT ELSE 0 END) AS '入国者数'
        ,SUM(CASE WHEN KIND_CODE = '120' THEN AMT ELSE 0 END) AS '出国者数'
        ,SUM(CASE WHEN KIND_CODE = '110' THEN AMT ELSE 0 END) -
         SUM(CASE WHEN KIND_CODE = '120' THEN AMT ELSE 0 END) AS '差分'
    from
        IMMIGRATION 
    INNER JOIN PORT
        ON PORT.PORT_CODE = IMMIGRATION.PORT_CODE
    WHERE
        GROUP_CODE = '120'
    group by
        IMMIGRATION.PORT_CODE
    )
where
    差分 > 0 
ORDER BY
      差分 desc
    , 港コード desc
;