select
    po.PORT_CODE as 港コード,
    po.PORT_NAME as 港名,
    am1.AMT as 入国者数,
    am2.AMT as 出国者数,
    am1.AMT - am2.AMT as 差分
from PORT as po
inner join IMMIGRATION as am1
    on po.PORT_CODE = am1.PORT_CODE and am1.GROUP_CODE = '120' and am1.KIND_CODE = '110'
inner join IMMIGRATION as am2
    on po.PORT_CODE = am2.PORT_CODE and am2.GROUP_CODE = '120' and am2.KIND_CODE = '120'
where  
    差分 > 0
order by 
    差分 desc,
    港コード desc;