select
    PORT_CODE as '港コード'
    ,PORT_NAME as '港名'
    ,POP_IN as '入国者数'
    ,POP_OUT as '出国者数'
    ,POP_IN-POP_OUT as '差分'
from (
select
    P.PORT_CODE
    ,S.PORT_NAME
    ,sum(
        case when KIND_CODE='110' then AMT end )
        as POP_IN
    ,sum(
        case when KIND_CODE='120' then AMT end )
        as POP_OUT
from
    IMMIGRATION P
    inner join
        PORT S
        on P.PORT_CODE=S.PORT_CODE
    inner join
        GRP G
        on G.GROUP_CODE=P.GROUP_CODE
where
    GROUP_NAME='外国人'
group by 1,2
) foo
where
    POP_IN-POP_OUT > 0
order by 5 desc, 1 desc
;