查看用户占用空间

1.查看当前用户每个表占用空间的大小：
Select Segment_Name,Sum(bytes)/1024/1024

From User_Extents

Group By Segment_Name

2.查看所有用户在每个表空间占用空间的大小：
Select owner,Tablespace_Name,Sum(bytes)/1024/1024
From Dba_Segments
Group By owner,Tablespace_Name

3.查看表空间剩余空间大小
select tablespace_name,sum(bytes)/1024/1024, sum(blocks)
from dba_free_space
group by tablespace_name;