with tmp as(
select
a.PORT_CODE as 港コード,
c.PORT_NAME as 港名,
max(case a.KIND_CODE when '110' then a.AMT end) as 入国者数,
max(case a.KIND_CODE when '120' then a.AMT end) as 出国者数
  from IMMIGRATION a
  join GRP b
    on b.GROUP_CODE = a.GROUP_CODE
  join PORT c
    on c.PORT_CODE = a.PORT_CODE
 where b.GROUP_NAME = '外国人'
group by a.PORT_CODE,c.PORT_NAME)
select 港コード,港名,入国者数,出国者数,
入国者数-出国者数 as 差分
  from tmp
order by 差分 desc,港コード