with base as(
select
    C.PORT_CODE as 港コード
,   C.PORT_NAME as 港名
,   case when B.KIND_CODE = 110 then B.AMT else 0 end as 入国者数
,   case when B.KIND_CODE = 120 then B.AMT else 0 end as 出国者数
from
    GRP A
,   IMMIGRATION B
,   PORT C
where
    A.GROUP_CODE = B.GROUP_CODE
and C.PORT_CODE = B.PORT_CODE
and A.GROUP_NAME = '外国人'
)
select
    A.港コード
,   A.港名
,   SUM(A.入国者数) as 入国者数
,   SUM(A.出国者数) as 出国者数
,   SUM(A.入国者数) - SUM(A.出国者数) as 差分
from
    base A
group by
    A.港コード
,   A.港名
having
    SUM(A.入国者数) > SUM(A.出国者数)
order by
    SUM(A.入国者数) - SUM(A.出国者数) DESC
,   A.港コード DESC