Oralce Oracle-XE でユーザーが使用できる容量を調べるには？

SELECT 
  t.TABLESPACE_NAME,
  t2.mb "全サイズMB",
  t3.mb "空サイズMB",
  DECODE(t2.mb - t3.mb,null,100,ROUND((t2.mb - t3.mb) / t2.mb * 100,2)) "使用率"
FROM
DBA_TABLESPACES t
  LEFT OUTER JOIN (
     SELECT TABLESPACE_NAME,ROUND(SUM(BYTES) / 1024 / 1024,1) mb FROM DBA_DATA_FILES
    GROUP BY TABLESPACE_NAME
  ) t2 ON t.tablespace_name = t2.tablespace_name
  LEFT OUTER JOIN (
    SELECT TABLESPACE_NAME,ROUND(SUM(BYTES)/ 1024 / 1024,1) mb FROM DBA_FREE_SPACE
    GROUP BY TABLESPACE_NAME ORDER BY TABLESPACE_NAME
  ) t3 ON t.tablespace_name = t3.tablespace_name
ORDER BY t2.mb DESC;