select PORT_CODE as '港コード',
       PORT_NAME as '港名',
       a1        as '入国者数',
       a2        as '出国者数',
       a1 - a2   as '差分'


from (
select IMM.PORT_CODE,                                                --as  '港コード',
             PORT_NAME,                                                    --as  '港名',
             coalesce(SUM(case when KIND_CODE = 110 then IMM.AMT else 0 end),0) as a1, -- as  '入国者数',
             coalesce(SUM(case when KIND_CODE = 120 then IMM.AMT else 0 end),0) as a2  -- as  '入国者数',
-- 外国人入国者のAMT - 外国人出国者のAMTの計算結果 as '差分'
      from IMMIGRATION IMM
               inner join PORT on IMM.PORT_CODE = PORT.PORT_CODE
      where IMM.GROUP_CODE=120

      group by IMM.PORT_CODE
      )
where a1>a2
order by 5 desc, 1 desc;