select 
PORT.PORT_CODE as '港コード',
PORT.PORT_NAME as '港名',
inpeople.AMT as '入国者数',
outpeople.AMT as '出国者数',
inpeople.AMT - outpeople.AMT as '差分'
from 
(
    select PORT_CODE,AMT 
    from IMMIGRATION,GRP 
    where IMMIGRATION.KIND_CODE='110'
    and IMMIGRATION.GROUP_CODE = GRP.GROUP_CODE
    and GRP.GROUP_NAME='外国人'
) inpeople,
(
    select PORT_CODE,AMT 
    from IMMIGRATION,GRP
    where KIND_CODE='120'
    and IMMIGRATION.GROUP_CODE = GRP.GROUP_CODE
    and GRP.GROUP_NAME='外国人'
) outpeople,
PORT
where inpeople.PORT_CODE = outpeople.PORT_CODE
and inpeople.PORT_CODE = PORT.PORT_CODE
and inpeople.AMT> outpeople.AMT
order by inpeople.AMT - outpeople.AMT desc,PORT.PORT_CODE desc