select
     agg.PORT_CODE as 港コード
    ,prt.PORT_NAME as 港名
    ,sum(agg.AMT) filter (where agg.KIND_CODE =  110) as 入国者数
    ,sum(agg.AMT) filter (where agg.KIND_CODE =  120) as 出国者数
    ,sum(agg.AMT) filter (where agg.KIND_CODE =  110)
      - sum(agg.AMT) filter (where agg.KIND_CODE =  120) as 差分
from
    IMMIGRATION as agg
inner join
    GRP as grp using(GROUP_CODE)
inner join
    PORT as prt using(PORT_CODE)
where
    agg.GROUP_CODE = '120'
group by
     agg.PORT_CODE
    ,prt.PORT_NAME
having
    sum(agg.AMT) filter (where agg.KIND_CODE =  110)
      > sum(agg.AMT) filter (where agg.KIND_CODE =  120)
order by
     差分 desc
    ,港コード desc