SELECT IM.PORT_CODE AS 港コード
      ,PORT_NAME AS 港名
      ,SUM (CASE KIND_CODE
         WHEN '110' THEN AMT 
         ELSE 0 END) AS 入国者数
      ,SUM (CASE KIND_CODE
         WHEN '120' THEN AMT 
         ELSE 0 END) AS 出国者数
      ,SUM (CASE KIND_CODE
         WHEN '110' THEN AMT 
         ELSE 0 END) - SUM (CASE KIND_CODE
         WHEN '120' THEN AMT 
         ELSE 0 END) AS 差分
FROM (SELECT PORT_CODE
             ,GROUP_CODE
             ,KIND_CODE
             ,AMT
        FROM IMMIGRATION 
        WHERE GROUP_CODE = '120'
        --GROUP BY PORT_CODE,KIND_CODE
        ) AS IM
JOIN PORT AS PO
  ON IM.PORT_CODE = PO.PORT_CODE
  
JOIN GRP
  ON IM.GROUP_CODE = GRP.GROUP_CODE
  GROUP BY IM.PORT_CODE--,IM.KIND_CODE
ORDER BY 差分 DESC,港コード DESC