select
 i.PORT_CODE as 港コード
 , p.PORT_NAME as 港名
 , t1.AMT as 入国者数
 , t2.AMT as 出国者数
 , t1.AMT - t2.AMT as 差分
from IMMIGRATION i
join (
 select 
  sum (i.AMT) as AMT
  , p.PORT_CODE
 from IMMIGRATION i
 join PORT p on p.PORT_CODE = i.PORT_CODE
 join GRP g on g.GROUP_CODE = i.GROUP_CODE
 where i.KIND_CODE = 110
 group by p.PORT_CODE
) t1 on i.PORT_CODE = t1.PORT_CODE
join (
 select 
  sum (i.AMT) as AMT
  , p.PORT_CODE
 from IMMIGRATION i
 join PORT p on p.PORT_CODE = i.PORT_CODE
 join GRP g on g.GROUP_CODE = i.GROUP_CODE
 where i.KIND_CODE = 120
 group by p.PORT_CODE
) t2 on i.PORT_CODE = t2.PORT_CODE
join PORT p on p.PORT_CODE = i.PORT_CODE
join GRP g on g.GROUP_CODE = i.GROUP_CODE
where t2.AMT < t1.AMT 
group by i.PORT_CODE
order by 差分 desc, i.PORT_CODE desc