select
    pt.port_code    as  '港コード'
,   pt.port_name    as  '港名'   
,   imin.in_amt    as  '入国者数'
,   imout.out_amt    as  '出国者数'
,   imin.in_amt - imout.out_amt    as  '差分'
from 
    port    pt
inner join
    (select
        it.port_code    as  port_code
    ,   sum(it.amt)     as  in_amt
    from
        immigration it
    where
        it.kind_code   =   '110'
    and it.group_code   =   '120'
    group by
        it.port_code
) imin
on
    pt.port_code    =   imin.port_code
inner join
    (select
        it.port_code    as  port_code
    ,   sum(it.amt)     as  out_amt
    from
        immigration it
    where
        it.kind_code   =   '120'
    and it.group_code   =   '120'
    group by
        it.port_code
) imout
on
    pt.port_code    =   imout.port_code
where
    imin.in_amt -   imout.out_amt > 0
order by
    imin.in_amt -   imout.out_amt   desc
,   pt.port_code    desc
;