select ig.port_code as 港コード,port_name as 港名,
    ig.amt as 入国者数,
    igout.amt as 出国者数,
    ig.amt - igout.amt as 差分
from immigration as ig
left outer join port as pt
on pt.port_code = ig.port_code
left outer join immigration as igout
on igout.port_code = ig.port_code 
and igout.group_code = ig.group_code
and igout.kind_code = '120'
where ig.kind_code = '110' and ig.amt >= igout.amt
order by 差分 desc,ig.port_code desc;