SELECT POR.PORT_CODE AS 港コード
      ,POR.PORT_NAME AS 港名
      ,IMM_IN.AMT  AS 入国者数
      ,IMM_OUT.AMT AS 出国者数
      ,(IMM_IN.AMT - IMM_OUT.AMT) AS 差分
FROM PORT POR
LEFT JOIN IMMIGRATION IMM_IN
ON  POR.PORT_CODE = IMM_IN.PORT_CODE
AND IMM_IN.KIND_CODE = 110
LEFT JOIN IMMIGRATION IMM_OUT
ON  POR.PORT_CODE = IMM_OUT.PORT_CODE
AND IMM_OUT.KIND_CODE = 120
LEFT JOIN GRP
ON  IMM_IN.GROUP_CODE = GRP.GROUP_CODE
WHERE GRP.GROUP_CODE = '120'
AND IMM_IN.AMT - IMM_OUT.AMT > 0
ORDER BY 差分 DESC
        ,港コード DESC