select
*,
入国者数 - 出国者数 as 差分
from
(
select
	P.PORT_CODE as 港コード,
	max(P.PORT_NAME) as 港名,
	sum(case when I.KIND_CODE = '110' then AMT else 0 end) 入国者数,
	sum(case when I.KIND_CODE = '120' then AMT else 0 end) 出国者数
from
	PORT P
inner join
	IMMIGRATION I
on
	P.PORT_CODE = I.PORT_CODE
	and
	I.KIND_CODE in ('110','120')
group by
    P.PORT_CODE
) A
where
入国者数 > 出国者数
order by 差分 desc, 港コード desc