select A.TABLESPACE_NAME,A.BYTES/(1024*1024*1024) "SPACE(G)",C.BYTES/(1024*1024) "FREE SPACE(M)",(C.BYTES*100)/A.BYTES "% FREE" FROM SYS.SM$TS_AVAIL A,SYS.SM$TS_FREE C WHERE A.TABLESPACE_NAME=C.TABLESPACE_NAME;

或者

select tablespace_name,sum(bytes)/(1024*1024*1024) "SPACE(G)" from dba_free_space group by tablespace_name;

（二）、用户

计算每个用户占用的磁盘空间

select owner,sum(bytes)/1024/1024/1024 "Space(G)" from dba_segments group by owner order by 2;

计算某个用户占用的磁盘空间

select owner,sum(bytes)/1024/1024/1024 "Space(G)" from dba_segments where owner='LIAOJL' group by owner;

（三）、表

Oracle都是以段为存储的，segment_name包含了表、索引、回滚段等，所以在dba_extents，dba_segments都可以找到占用空间大小的信息。

select sum(bytes)/1024/1024 "Space(M)" from dba_extents where owner='LIAOJL' and segment_name='STUDENTS';

dba_segments也可以计算表的大小：

select segment_name,bytes/1024/1024 "Space(MB)" from dba_segments where SEGMENT_TYPE='TABLE' and segment_name=upper('你要查找的表的名字');

当时上面的写法不完全正确，当表是分区表，dba_segments有多条信息，可改成：

select segment_name,sum(bytes)/1024/1024 "Space(MB)" from dba_segments where segment_name=upper('你要查找的表的名字');

上述方法对于一个很大的数据库，sql语句执行起来会很慢，而且消耗数据库资源。Oracle支持对表进行分析，执行分析表操作后可以在dba_tables等系统表中查询表大小、行数等信息，不过这些信息不是实时更新的，可以在数据库空闲时，通过计划任务来更新。

分析sql方法：

analyze table tab_name compute statistics;

表太大的话可以执行：

analyze table tab_name estimate statistics;

/*SELECT tablespace_name,sum ( blocks ) as free_blk,

　　trunc ( sum ( bytes ) /(1024*1024) ) as free_m,

　　max ( bytes ) / (1024) as big_chunk_k,count (*) as num_chunks

　　FROM dba_free_space GROUP BY tablespace_name;*/ /* * sqlName: obj_seg * 2006-11-17 By HuiYi * 查詢對象大小 */ select owner,sum(bytes)/1024/1024/1024 "Space(G)" from dba_segments group by owner order by 2 desc