SELECT
    i.PORT_CODE AS 港コード
    ,PORT_NAME AS 港名
    ,i.AMT AS 入国者数
    ,i120.AMT AS 出国者数
    ,i.AMT - i120.AMT AS 差分
FROM
    IMMIGRATION AS i
JOIN
    PORT AS p
ON
    i.PORT_CODE = p.PORT_CODE
JOIN
    GRP AS g
ON
    i.GROUP_CODE = g.GROUP_CODE
JOIN
    (SELECT
        PORT_CODE
        ,AMT
    FROM
        IMMIGRATION
    WHERE
        KIND_CODE = 120) AS i120
ON
    i.PORT_CODE = i120.PORT_CODE
WHERE
    GROUP_NAME = '外国人'
    AND KIND_CODE = 110
    AND i.AMT > i120.AMT
ORDER BY 
    差分 DESC
    ,港コード DESC;