SELECT
    IMG.PORT_CODE AS '港コード'
    ,PORT.PORT_NAME AS '港名'
    ,IMG.AMT AS '入国者数'
    ,IMG2.AMT AS '出国者数'
    ,(IMG.AMT - IMG2.AMT) AS '差分'
FROM IMMIGRATION AS IMG
INNER JOIN IMMIGRATION AS IMG2
    ON IMG2.PORT_CODE = IMG.PORT_CODE
    AND IMG2.GROUP_CODE = IMG.GROUP_CODE
    AND IMG2.KIND_CODE = '120'
INNER JOIN PORT
    ON PORT.PORT_CODE = IMG.PORT_CODE

WHERE IMG.KIND_CODE = '110'
AND IMG.GROUP_CODE = '120'
AND 差分 > 0

ORDER BY 差分 DESC
,IMG.PORT_CODE DESC