select b.tablespace_name, sum(b.bytes)/(1024*1024)
from dba_data_files b 
where b.bytes < 2097152 
and b.tablespace_name not in (select distinct c.default_tablespace from dba_users c)
and b.tablespace_name not in (select distinct d.tablespace_name from dba_segments d)
group by b.tablespace_name order by 2;