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
;