select * from (
select PORT_CODE AS '港コード',
       PORT_NAME AS '港名',
       SUM(case when GROUP_CODE = '120' and KIND_CODE = '110' THEN AMT END) AS '入国者数',
       SUM(case when GROUP_CODE = '120' and KIND_CODE = '120' THEN AMT END) AS '出国者数',
       SUM(case when GROUP_CODE = '120' and KIND_CODE = '110' THEN AMT END) - SUM(case when GROUP_CODE = '120' and KIND_CODE = '120' THEN AMT END) AS '差分'
from  IMMIGRATION
left outer join PORT USING(PORT_CODE)
group by PORT_CODE,PORT_NAME
)
where 差分 > 0
;