select
    im.PORT_CODE as 港コード
  , im.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
  , SUM(case when KIND_CODE = '110' then AMT else 0 end) - SUM(case when KIND_CODE = '120' then AMT else 0 end) as 差分
from
           IMMIGRATION im
inner join PORT        po
        on im.PORT_CODE  = po.PORT_CODE
inner join GRP gr
        on im.GROUP_CODE = gr.GROUP_CODE
where
    gr.GROUP_NAME = '外国人'
group by
    PORT_CODE
having
    差分 > 0
order by
    年齢コード ASC
;