select 
    pr.PORT_CODE AS '港コード',
    pr.PORT_NAME AS '港名',
    sum(im1.AMT)  AS '入国者数',
    sum(im2.AMT)  AS '出国者数',
    sum(im1.AMT) - sum(im2.AMT) AS '差分'
from
    PORT pr 
    JOIN IMMIGRATION AS im1
    on pr.PORT_CODE = im1.PORT_CODE
    and im1.KIND_CODE = '110'
    JOIN IMMIGRATION AS im2
    on pr.PORT_CODE = im2.PORT_CODE
    and im2.KIND_CODE = '120'
    and im1.AMT > im2.AMT
    group by pr.PORT_CODE
    order by 5 desc, pr.PORT_CODE desc