登录sqlplus：

cmd命令行登录：sqlplus orcl/orcl as sysdba

查询表空间使用率

select b.file_id　　文件ID,

b.tablespace_name　　表空间,

b.file_name　　　　　物理文件名,

b.bytes　　　　　　　总字节数,

(b.bytes-sum(nvl(a.bytes,0)))　　　已使用,

sum(nvl(a.bytes,0))　　　　　　　　剩余,

sum(nvl(a.bytes,0))/(b.bytes)*100　剩余百分比

from dba_free_space a,dba_data_files b

where a.file_id=b.file_id

group by b.tablespace_name,b.file_name,b.file_id,b.bytes

order by b.tablespace_name

select tablespace_name, segment_name, bytes / 1024 / 1024    from user_segments  where segment_type = ‘TABLE‘    and tablespace_name = ‘VNOX‘  order by bytes desc ;

1, dba_data_files,dba_segments,dba_free_space

得出结论:一般情况下(没有drop表的时候):dba_data_files bytes = (dba_segments bytes + dba_free_space bytes)

实验:

SQL> Select sum(bytes)/1024/1024/1024 from dba_segments;

SUM(BYTES)/1024/1024/1024

-------------------------

1.58441162

SQL> select sum(bytes)/1024/1024/1024 from dba_free_space;

SUM(BYTES)/1024/1024/1024

-------------------------

.323669434

SQL> select sum(bytes)/1024/1024/1024 from dba_data_files;

SUM(BYTES)/1024/1024/1024

-------------------------

1.9140625

原文：https://www.cnblogs.com/nieyuqin/p/10622676.html