WITH IMM AS (
    SELECT
        IM.PORT_CODE AS "港コード"
        ,PORT.PORT_NAME AS "港名"
        ,MAX(CASE KIND_CODE WHEN '110' THEN AMT ELSE 0 END) AS "入国者数"
        ,MAX(CASE KIND_CODE WHEN '120' THEN AMT ELSE 0 END) AS "出国者数"
    FROM
        IMMIGRATION AS IM
    INNER JOIN
        PORT ON (IM.PORT_CODE = PORT.PORT_CODE) 
    WHERE
        GROUP_CODE = '120'
    GROUP BY
        IM.PORT_CODE
)
SELECT
    "港コード"
    ,"港名"
    ,"入国者数"
    ,"出国者数"
    ,("入国者数" - "出国者数") AS "差分"
FROM
    IMM
WHERE
    "差分" > 0
ORDER BY
    "差分" DESC
    ,"港コード" DESC
;