select
 PORT.PORT_CODE as '港コード',
 PORT_NAME as '港名',
 sum(case GRP.GROUP_CODE when 110 then AMT else 0 end) as '入国者数',
 sum(case GRP.GROUP_CODE when 120 then AMT else 0 end) as '出国者数',
 sum(case GRP.GROUP_CODE when 110 then AMT else 0 end)-sum(case GRP.GROUP_CODE when 120 then AMT else 0 end) as '差分'
 from IMMIGRATION
  inner join PORT
  on IMMIGRATION.PORT_CODE = PORT.PORT_CODE
  inner join GRP
  on IMMIGRATION.GROUP_CODE = GRP.GROUP_CODE
  group by PORT.PORT_NAME