select
  PORT.PORT_CODE as "港コード",
  PORT.PORT_NAME as "港名",
  A.AMT as "入国者数",
  B.AMT as "出国者数",
  (A.AMT - B.AMT) as "差分"
from
  (select PORT_CODE, AMT from IMMIGRATION where KIND_CODE = '110' group by PORT_CODE) as A
  inner join (select PORT_CODE, AMT  from IMMIGRATION where KIND_CODE = '120' group by PORT_CODE) as B on B.PORT_CODE = A.PORT_CODE
  inner join PORT on PORT.PORT_CODE = A.PORT_CODE 
where
  A.AMT > B.AMT
group by 
  PORT.PORT_CODE, PORT.PORT_NAME
order by 
  5 desc, 1 desc

--外国人の入国者が出国者より多い港を抽出しなさい。 種別コードは、'110'(入国者) 、'120'(出国者)となる。