WITH tmp AS(
    SELECT
        IM.PORT_CODE
        ,PT.PORT_NAME
        ,CASE
            WHEN IM.GROUP_CODE = 110 THEN AMT
        ELSE 0
        END AS 入国者数
        ,CASE
            WHEN IM.GROUP_CODE = 120 THEN AMT
        ELSE 0
        END AS 出国者数
    FROM
        IMMIGRATION AS IM
    INNER JOIN PORT AS PT
        ON IM.PORT_CODE = PT.PORT_CODE
)
SELECT
   PORT_CODE AS 港コード
   ,PORT_NAME AS 港名
   ,SUM(入国者数) AS 入国者数
   ,SUM(出国者数) AS 出国者数
   ,SUM(入国者数) - SUM(出国者数) AS 差分
FROM tmp
GROUP BY 1,2
ORDER BY 差分 DESC ,港コード DESC