select 
    I.PORT_CODE as 港コード
    ,P.PORT_NAME as 港名
    ,I2.N_IN as 入国者数
    ,I3.N_OUT as 出国者数
    ,abs(I2.N_IN - I3.N_OUT) as 差分
from
    IMMIGRATION as I
left join PORT as P
on I.PORT_CODE = P.PORT_CODE
left join 
    (
        select 
            PORT_CODE
            ,sum(AMT) as N_IN
        from 
            IMMIGRATION
        where
            GROUP_CODE = '120' --外国人
            and KIND_CODE = '110' --入国者
        group by PORT_CODE, KIND_CODE
    ) as I2
on I.PORT_CODE = I2.PORT_CODE
left join 
    (
        select 
            PORT_CODE
            ,sum(AMT) as N_OUT
        from 
            IMMIGRATION
        where
            GROUP_CODE = '120' --外国人
            and KIND_CODE = '120' --出国者
        group by PORT_CODE, KIND_CODE
    ) as I3
on I.PORT_CODE = I3.PORT_CODE
where I2.N_IN > I3.N_OUT
group by I.PORT_CODE
order by 差分 desc, 港コード desc