select *
	,入国者数 - 出国者数 as 差分
from (
select a.PORT_CODE as 港コード
	,b.PORT_NAME as 港名
	,SUM(CASE WHEN KIND_CODE = 110 THEN AMT ELSE 0 END) as 入国者数
	,SUM(CASE WHEN KIND_CODE = 120 THEN AMT ELSE 0 END) as 出国者数
from IMMIGRATION as a
INNER JOIN PORT as b
on a.PORT_CODE = b.PORT_CODE
WHERE GROUP_CODE = 120
GROUP BY 1,2
)
where 入国者数 > 出国者数
order by 5 DESC,1 DESC
;