with tbl as (
    select
        i.PORT_CODE
        ,p.PORT_NAME
        ,case when KIND_CODE = '110' and GROUP_CODE = '120' then i.AMT else 0 end as "in"
        ,case when KIND_CODE = '120' and GROUP_CODE = '120' then i.AMT else 0 end as "out"
    from
        IMMIGRATION as i
    left join
        PORT as p
    on 
        p.PORT_CODE = i.PORT_CODE
)
select
    PORT_CODE as "港コード"
    ,PORT_NAME as "港名"
    ,sum("in") as "入国者数"
    ,sum("out") as "出国者数"
    ,sum("in")- sum("out") as "差分"
from
    tbl
group by
    1, 2
having
    "差分" > 0
order by
    "差分" DESC
    ,PORT_CODE DESC;