SELECT PT.PORT_CODE AS 港コード
      ,PT.PORT_NAME AS 港名
      ,INC.TOTAL_AMT AS 入国者数
      ,OUTC.TOTAL_AMT AS 出国者数
      ,(INC.TOTAL_AMT - OUTC.TOTAL_AMT) AS 差分
  FROM PORT PT
  LEFT OUTER JOIN (SELECT IM.PORT_CODE
                         ,SUM(1.0 * IFNULL(IM.AMT, 0)) AS TOTAL_AMT
                     FROM IMMIGRATION IM
                    INNER JOIN GRP
                       ON IM.GROUP_CODE = GRP.GROUP_CODE
                    WHERE GRP.GROUP_CODE = '120'
                      AND IM.KIND_CODE = '110'
                    GROUP BY IM.PORT_CODE) AS INC
    ON PT.PORT_CODE = INC.PORT_CODE
  LEFT OUTER JOIN (SELECT IM.PORT_CODE
                         ,SUM(1.0 * IFNULL(IM.AMT, 0)) AS TOTAL_AMT
                     FROM IMMIGRATION IM
                    INNER JOIN GRP
                       ON IM.GROUP_CODE = GRP.GROUP_CODE
                    WHERE GRP.GROUP_CODE = '120'
                      AND IM.KIND_CODE = '120'
                    GROUP BY IM.PORT_CODE) AS OUTC
    ON PT.PORT_CODE = OUTC.PORT_CODE
 WHERE INC.TOTAL_AMT > OUTC.TOTAL_AMT
 ORDER BY 差分 DESC, 港コード DESC