默认的，一个表当进行truncate 表时DATA_OBJECT_ID将增加1；
但是当此表有一个索引时，进行truncate 表时DATA_OBJECT_ID将增加2：

SQL>
SQL> create table x ( x number );

Table created.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779899 01-JUL-14    01-JUL-14

SQL>  truncate table x;

Table truncated.

SQL>  select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779899 01-JUL-14    01-JUL-14

SQL> insert into x values ( 1 );

1 row created.

SQL> commit;

Commit complete.

SQL> select count(1) from x;

  COUNT(1)
----------
         1

SQL>  select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779899 01-JUL-14    01-JUL-14

SQL> truncate table x;

Table truncated.

SQL>  select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779900 01-JUL-14    01-JUL-14

SQL> truncate table x;

Table truncated.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779900 01-JUL-14    01-JUL-14

SQL>  insert into x values ( 1 );

1 row created.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779900 01-JUL-14    01-JUL-14

SQL> commit;

Commit complete.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779900 01-JUL-14    01-JUL-14

SQL> truncate table x;

Table truncated.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779901 01-JUL-14    01-JUL-14

SQL>
SQL>
SQL>
SQL> create index kk on x(x);

Index created.

SQL>  select count(1) from x;

  COUNT(1)
----------
         0

SQL> insert into x values ( 1 );

1 row created.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779901 01-JUL-14    01-JUL-14

SQL> commit;

Commit complete.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779901 01-JUL-14    01-JUL-14

SQL> truncate table x;

Table truncated.

SQL> select object_id, data_object_id, last_ddl_time, created from user_objects where object_name = 'X';

 OBJECT_ID DATA_OBJECT_ID LAST_DDL_TIM CREATED
---------- -------------- ------------ ------------
    779899         779904 01-JUL-14    01-JUL-14