object_id与data_object_id的关系

object_id和data_object_id都是表示数据库对象的唯一标志。
 
object_id是数据库对象的逻辑id
data_object_id是数据库对象的物理id
 
如果一些object没有物理属性的话那它就不存在data_object_id，例如procedure,function,package,data type,db link,mv定义，view定义，临时表，分区表定义等等这些object都是没有对应着某个segment，因此它们的data_object_id都为空。
 
当一个表建立的时候，他的object_id 和 data_object_id是相等的。当表move和truncate后data_object_id会发生变化。修改表结构不会更改。

SQL> create table ldy.obid as select rownum as "rn" from dba_objects;

表已创建。

SQL> select object_id,data_object_id from dba_objects where object_name='OBID' and owner='LDY';

 OBJECT_ID DATA_OBJECT_ID
---------- --------------
     12436          12436
    
SQL> select header_file,header_block,blocks from dba_segments where segment_name='OBID' and owner='LDY';

HEADER_FILE HEADER_BLOCK     BLOCKS
----------- ------------ ----------
          7       190347         24    
         
         
SQL> alter table ldy.obid move;

表已更改。

SQL> select object_id,data_object_id from dba_objects where object_name='OBID' and owner='LDY';

 OBJECT_ID DATA_OBJECT_ID
---------- --------------
     12436          12437

表经过move后，物理ID发生变化.

SQL> select header_file,header_block,blocks from dba_segments where segment_name='OBID' and owner='LDY';

HEADER_FILE HEADER_BLOCK     BLOCKS
----------- ------------ ----------
          7       190371         24

SQL> truncate table ldy.obid;

表被截断。

SQL> select object_id,data_object_id from dba_objects where object_name='OBID' and owner='LDY';

 OBJECT_ID DATA_OBJECT_ID
---------- --------------
     12436          12438

SQL> select header_file,header_block,blocks from dba_segments where segment_name='OBID' and owner='LDY';

HEADER_FILE HEADER_BLOCK     BLOCKS
----------- ------------ ----------
          7       190371          8

表经过truncate 后 物理ID也发生变化。

SQL> alter table ldy.obid add (n number);

表已更改。

SQL> select object_id,data_object_id from dba_objects where object_name='OBID' and owner='LDY';

 OBJECT_ID DATA_OBJECT_ID
---------- --------------
     12436          12438

SQL> select header_file,header_block,blocks from dba_segments where segment_name='OBID' and owner='LDY';

HEADER_FILE HEADER_BLOCK     BLOCKS
----------- ------------ ----------
          7       190371          8         

给表增加一个列，也没发生变化

所以总上所简述

只有当segment发生变化时data_object_id才发生变化

有时候我们根据rowid 算时得到的data_object_id会误以为就是object_id,因为要是没有发生segment变化时

两者值是相等的