SELECT
    X.港コード
    , P.PORT_NAME AS 港名
    , X.入国者数
    , X.出国者数
    , X.入国者数 - X.出国者数 AS 差分
FROM
    (
        SELECT
            I.PORT_CODE AS 港コード
            , SUM(
                CASE
                    WHEN
                        KIND_CODE = '110'
                        THEN
                            I.AMT
                        ELSE
                            0
                END
            ) AS 入国者数
            , SUM(
                CASE
                    WHEN
                        KIND_CODE = '120'
                        THEN
                            I.AMT
                        ELSE
                            0
                END
            ) AS 出国者数
        FROM
            IMMIGRATION AS I
        WHERE
            1=1
            AND I.GROUP_CODE = '120'
        GROUP BY
            I.PORT_CODE
    ) AS X
LEFT OUTER JOIN
    PORT AS P
    ON 1=1
    AND X.港コード = P.PORT_CODE
ORDER BY
    差分 DESC
    , X.港コード DESC