SELECT a.tablespace_name, "Free, MB", "Total, MB" FROM
(SELECT tablespace_name, ROUND(SUM(bytes)/1024/1024) AS "Total, MB" FROM dba_data_files GROUP BY tablespace_name
UNION
SELECT tablespace_name, ROUND(SUM(bytes)/1024/1024) AS "Total, MB" FROM dba_temp_files GROUP BY tablespace_name) a,
(SELECT tablespace_name, ROUND(SUM(bytes)/1024/1024) AS "Free, MB" FROM dba_free_space GROUP BY tablespace_name) b
WHERE a.tablespace_name = b.tablespace_name (+)
ORDER BY a.tablespace_name;