select
    I.PORT_CODE as 港コード,
    P.PORT_NAME as 港名,
    入国者数,
    出国者数,
    入国者数 - 出国者数 as 差分
From 
    PORT P,
    (Select PORT_CODE,AMT as 入国者数 From IMMIGRATION I Where KIND_CODE = 110) as I,
    (Select PORT_CODE,AMT as 出国者数 From IMMIGRATION I Where KIND_CODE = 120) as O
where 
    I.PORT_CODE = P.PORT_CODE
    AND O.PORT_CODE = P.PORT_CODE
    AND 入国者数 > 出国者数
order by
    差分 desc
    , 港コード desc