SQL>
SQL> select owner, tablespace_name, sum(bytes)/(1024*1024) total_meg
2 from dba_extents
3 where rownum < 50
4 group by rollup (owner,tablespace_name)
5 /
OWNER TABLESPACE_NAME TOTAL_MEG
------------------------------ ------------------------------ ----------
SYS SYSTEM 4
SYS 4
4
SQL>