select
i.PORT_CODE as 港コード,
p.PORT_NAME as 港名,
sum(AMT) as 入国者数,
ii.出国者数 as 出国者数,
sum(AMT) - ii.出国者数 as 差分
from IMMIGRATION i
join PORT p on i.PORT_CODE = p.PORT_CODE
join
    (
    select
        PORT_CODE,
        sum(AMT) as 出国者数
    from IMMIGRATION
    where KIND_CODE = 120
    group by PORT_CODE
    ) as ii
    on i.PORT_CODE = ii.PORT_CODE
where KIND_CODE = 110
group by i.PORT_CODE
having 差分 > 0
order by 差分 DESC, i.PORT_CODE DESC