SELECT
    a.PORT_CODE AS 港コード
    , c.PORT_NAME AS 港名
    , a.SUM_AMT_IN AS 入国者数
    , b.SUM_AMT_OUT AS 出国者数
    , a.SUM_AMT_IN - b.SUM_AMT_OUT AS 差分
FROM
    (
        SELECT
            PORT_CODE
            , SUM(AMT) AS SUM_AMT_IN
        FROM
            IMMIGRATION
        WHERE
            GROUP_CODE = 120
        AND
            KIND_CODE = 110
        GROUP BY
            PORT_CODE
    ) AS a
INNER JOIN
    (
        SELECT
            PORT_CODE
            , SUM(AMT) AS SUM_AMT_OUT
        FROM
            IMMIGRATION
        WHERE
            GROUP_CODE = 120
        AND
            KIND_CODE = 120
        GROUP BY
            PORT_CODE
    ) AS b
ON 
    a.PORT_CODE = b.PORT_CODE
AND
    a.SUM_AMT_IN > b.SUM_AMT_OUT
INNER JOIN
    PORT AS c
ON 
    a.PORT_CODE = c.PORT_CODE
ORDER BY
    差分 DESC
    , 港コード DESC