SELECT DISTINCT
    IM.PORT_CODE AS 港コード,
    PT.PORT_NAME AS 港名,
    入国者.AMT AS 入国者数,
    出国者.AMT AS 出国者数,
    入国者.AMT - 出国者.AMT AS 差分
FROM IMMIGRATION AS IM
RIGHT JOIN PORT AS PT ON PT.PORT_CODE = 港コード
RIGHT JOIN 
    (SELECT
        PORT_CODE,
        AMT
    FROM IMMIGRATION
    WHERE KIND_CODE = '110'
    ) AS 入国者 ON 入国者.PORT_CODE = 港コード
RIGHT JOIN 
    (SELECT
        PORT_CODE,
        AMT
    FROM IMMIGRATION
    WHERE KIND_CODE = '120'
    ) AS 出国者 ON 出国者.PORT_CODE = 港コード
WHERE
    IM.GROUP_CODE = '120'
    AND 入国者.AMT > 出国者.AMT
ORDER BY
    差分 DESC,
    港コード DESC;