如何查看oracle表空间已使用大小
1.查看所有表空间大小：

select a.tablespace_name,total,free,total-free used from ( select tablespace_name,sum(bytes)/1024/1024 total from dba_data_files   group by tablespace_name) a, ( select tablespace_name,sum(bytes)/1024/1024 free from dba_free_space   group by tablespace_name) bwhere a.tablespace_name=b.tablespace_name;