select 
    p.PORT_CODE 港コード,
    p.PORT_NAME 港名,
    intbl.inamt 入国者数,
    outtbl.outamt 出国者数,
    intbl.inamt - outtbl.outamt 差分
from
    (
    select PORT_CODE,sum(amt) inamt
    from IMMIGRATION
    where kind_code = '110'
    group by PORT_CODE) intbl
inner join
    (
    select PORT_CODE,sum(amt) outamt
    from IMMIGRATION
    where kind_code = '120'
    group by PORT_CODE) outtbl
on intbl.PORT_CODE = outtbl.PORT_CODE
inner join
    port p
on p.PORT_CODE = intbl.PORT_CODE 
and p.PORT_CODE = outtbl.PORT_CODE 
where 入国者数 > 出国者数 
order by 差分 desc, 港コード desc;