with tmp as (
select
    p.port_code as "港コード"
    ,p.port_name as "港名"
    ,sum(case when i.kind_code = '110' then amt else 0 end) as "入国者数"
    ,sum(case when i.kind_code = '120' then amt else 0 end) as "出国者数"
from
    immigration i 
    left join port p on i.port_code = p.port_code
    left join grp g on i.group_code = g.group_code
where
    g.group_code = '120'
group by
    p.port_code, p.port_name
)
select
    *
    ,"入国者数" - "出国者数" as "差分"
from
    tmp
where
    "入国者数" - "出国者数" > 0
order by
    "差分" desc, "港コード" desc
;