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