SELECT
    PT.PORT_CODE AS '港コード'
    ,PT.PORT_NAME AS '港名'
    ,IMG_IN.AMT AS '入国者数'
    ,IMG_OUT.AMT AS '出国者数'
    ,IMG_IN.AMT - IMG_OUT.AMT AS '差分'
FROM
    PORT AS PT 
    LEFT OUTER JOIN IMMIGRATION AS IMG_IN ON(PT.PORT_CODE = IMG_IN.PORT_CODE AND IMG_IN.GROUP_CODE = '120' AND IMG_IN.KIND_CODE = '110' )
    LEFT OUTER JOIN IMMIGRATION AS IMG_OUT ON(PT.PORT_CODE = IMG_OUT.PORT_CODE AND IMG_OUT.GROUP_CODE = '120' AND IMG_OUT.KIND_CODE = '120' )
WHERE
    IMG_IN.AMT > IMG_OUT.AMT
ORDER BY
    IMG_IN.AMT - IMG_OUT.AMT DESC
    ,PT.PORT_CODE