SELECT IM.PORT_CODE AS 港コード
       , PT.PORT_NAME AS 港名
       , SUM(CASE WHEN IM.KIND_CODE = '110' THEN IM.AMT END ) AS 入国者数
       , SUM(CASE WHEN IM.KIND_CODE = '120' THEN IM.AMT END ) AS 出国者数
       , SUM(CASE WHEN IM.KIND_CODE = '110' THEN IM.AMT END) -  SUM(CASE WHEN IM.KIND_CODE = '120' THEN IM.AMT END) AS 差分

  FROM IMMIGRATION AS IM
 INNER JOIN PORT AS PT
    ON PT.PORT_CODE = IM.PORT_CODE
 WHERE IM.GROUP_CODE = '120'
 GROUP BY IM.PORT_CODE
          , PT.PORT_NAME
 ORDER BY SUM(CASE WHEN IM.KIND_CODE = '110' THEN IM.AMT END) -  SUM(CASE WHEN IM.KIND_CODE = '120' THEN IM.AMT END) DESC
          , IM.PORT_CODE DESC;