Oracle DB , 计算各个用户/schema 的磁盘占用空间

http://www.dba-oracle.com/t_find_size_schema.htm

Question:  How do I find the size of a schema in my database?

Answer: It depends on how you define "size".  If you want the total disk space consumed by the schema (including indexes, tablespace free space), then the SQL query is quite simple:

select 
   owner,
   sum(bytes)/1024/1024/1024 schema_size_gig
from 
   dba_segments 
group by 
   owner;

If you just want the size of the schema in terms of the space consumed by table rows, you would use a different query to calculate the schema size:

select 
   sum(bytes)/1024/1024/1024 as size_in_gig, 
   segment_type
from 
   dba_segments
where 
   owner='SCOTT' 
group by 
   segment_type;

Drop Table 之后，如果空间不能回收，需要执行西面语句

  清除当前用户的回收站：purge recyclebin;

  清除所有用户的回收站：purge dba_recyclebin;