SELECT DISTINCT
    PORT.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 IMMIGRATION.PORT_CODE = PORT.PORT_CODE 
    INNER JOIN GRP
        ON IMMIGRATION.GROUP_CODE  = GRP.GROUP_CODE  
WHERE
   差分 > 0
   
GROUP BY PORT.PORT_CODE

ORDER BY
    差分 DESC
    , 港コード DESC;