SELECT
    PORT.PORT_CODE AS 港コード
    , PORT.PORT_NAME AS 港名
    , IM.AMT AS 入国者数
    , IMOUT.AMT AS 出国者数
    , (IM.AMT - IMOUT.AMT) AS 差分
FROM IMMIGRATION IM
    INNER JOIN PORT
        ON IM.PORT_CODE = PORT.PORT_CODE
    INNER JOIN GRP
        ON IM.GROUP_CODE = GRP.GROUP_CODE
    INNER JOIN IMMIGRATION IMOUT
        ON IMOUT.PORT_CODE = IM.PORT_CODE
        AND IMOUT.GROUP_CODE = IM.GROUP_CODE
        AND IMOUT.KIND_CODE = '120'
WHERE IM.KIND_CODE = '110' 
    AND (IM.AMT - IMOUT.AMT) >= 0
ORDER BY 差分 DESC, 港コード DESC;