查看表空间下用户表的大小(GB）

所占空间由大到小的前三十的数据表：

select * from (
select segment_name,bytes/1024/1024/1024 as GB from dba_segments where owner = USER order by bytes desc 
               ) 
where rownum <= 30

查询表名为table_name的数据表大小

select round(BYTES/1024/1024/1024,2)||'GB' from user_segments where segment_name=table_name