select IG.PORT_CODE AS 港コード
    , PORT.PORT_NAME AS 港名
    , (case when (IG.GROUP_CODE=120 and IG.KIND_CODE=110) then IG.AMT end) AS '入国者数'
    , (case when (IG.GROUP_CODE=120 and IG.KIND_CODE=120) then IG.AMT end) AS '出国者数'
    , ('入国者数'-'出国者数') AS 差分
from IMMIGRATION AS IG1
    inner join IMMIGRATION AS IG2
    on IG1.PORT_CODE = IG2.PORT_CODE
    and IG1.GROUP_CODE = IG2.GROUP_CODE
    and IG.KIND_CODE=120
    inner join PORT
    on IG.PORT_CODE = PORT.PORT_CODE
where IG.GROUP_CODE=120 and IG.KIND_CODE=110 and 差分>0
group by IG.PORT_CODE
order by 差分 desc
    , IG.PORT_CODE desc;