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SELECT   a.tablespace_name,
         ROUND(a.BYTES, 2) "已使用(G)",
         ROUND(b.BYTES, 2) "未使用(G)",
         ROUND(((a.BYTES - b.BYTES) / a.BYTES) * 100, 2) "使用率%"
FROM     (SELECT   tablespace_name,
                   SUM(BYTES) /(1024 * 1024 * 1024) BYTES
          FROM     dba_data_files
          GROUP BY tablespace_name) a,
         (SELECT   tablespace_name,
                   SUM(BYTES) /(1024 * 1024 * 1024) BYTES
          FROM     dba_free_space
          GROUP BY tablespace_name) b
WHERE    a.tablespace_name = b.tablespace_name
ORDER BY ((a.BYTES - b.BYTES) / a.BYTES) DESC;