select
a.port_code as "港コード"
,c.port_name as "港名"
,a.amt as "入国者数"
,b.amt as "出国者数"
,(a.amt - b.amt) as "差分"
from
immigration a
inner join
immigration b
on
a.port_code = b.port_code
and a.group_code = b.group_code
and b.kind_code = '120'
inner join 
port c
on
a.port_code = c.port_code
where
a.group_code = '120'
and a.kind_code = '110'
and "差分" > 0
order by
"差分" desc
,"港コード" desc
;