Prova detta:
-- Available space, by tablespace
SELECT * FROM
(SELECT tablespace_name FROM dba_tablespaces)
LEFT OUTER JOIN
(SELECT tablespace_name, SUM(bytes) AS total_bytes
FROM dba_data_files
GROUP BY tablespace_name)
USING (tablespace_name)
LEFT OUTER JOIN
(SELECT tablespace_name, sum(bytes) AS used_bytes
from dba_segments
GROUP BY tablespace_name)
USING (tablespace_name)
LEFT OUTER JOIN
(SELECT tablespace_name, SUM(bytes) AS free_bytes
FROM dba_free_space
GROUP BY tablespace_name)
USING (tablespace_name);