with TRGT as (
  select
    I.*
  from
    IMMIGRATION I
      inner join GRP G on I.GROUP_CODE = G.GROUP_CODE
  where G.GROUP_NAME = '外国人'
)
select
  T1.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
  TRGT T1
    inner join TRGT T2 on T1.PORT_CODE = T2.PORT_CODE and T1.KIND_CODE < T2.KIND_CODE
    inner join PORT P on T1.PORT_CODE = P.PORT_CODE
where T1.AMT > T2.AMT
order by
  "差分" desc,
  "港コード" desc
;