DELETE statement executed even using set autotrace traceonly explain

Normally, when you issue 'set autotrace traceonly explain', then execute the SQL statement in order to get its execution plan, the SQL won't get executed actually. However, I realized that this is not true for 'DELETE' statement. Below is a test case:

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - 64bi
PL/SQL Release 10.2.0.1.0 - Production
CORE    10.2.0.1.0      Production
TNS for Solaris: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production

SQL>
SQL> drop table t;

Table dropped.

SQL>
SQL> create table t
  2  as
  3  select rownum id,
  4    a.*
  5  from all_objects a where rownum <= 1000;

Table created.

SQL>
SQL> create index  t_ix on t(id);

Index created.

SQL>
SQL> execute dbms_stats.gather_table_stats(user,'t', cascade=>true);

PL/SQL procedure successfully completed.

SQL>
SQL> select count(*) from t;

  COUNT(*)
----------
      1000

SQL>
SQL>
SQL> set autotrace traceonly explain
SQL> delete from t where  id >=500;

501 rows deleted.


Execution Plan
----------------------------------------------------------
Plan hash value: 2466302700

--------------------------------------------------------------------------
 Id   Operation          Name  Rows   Bytes  Cost (%CPU) Time   
--------------------------------------------------------------------------
   0  DELETE STATEMENT           502   2008      3   (0) 00:00:01
   1   DELETE            T                                      
*  2    INDEX RANGE SCAN T_IX    502   2008      3   (0) 00:00:01
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("ID">=500)

SQL>
SQL> set autotrace off
SQL>
SQL> select count(*) from t;

  COUNT(*)
----------
       499

I also tested "explain plan for". We see the delete statement is not actually executed in this case.

SQL>
SQL> explain plan for
  2  delete from t;

Explained.


PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
Plan hash value: 2034385699

---------------------------------------------------------------------------
 Id   Operation           Name  Rows   Bytes  Cost (%CPU) Time   
---------------------------------------------------------------------------
   0  DELETE STATEMENT           1000   4000      5   (0) 00:00:01
   1   DELETE             T                                      
   2    TABLE ACCESS FULL T      1000   4000      5   (0) 00:00:01
---------------------------------------------------------------------------

9 rows selected.

SQL> select count(*) from t;

  COUNT(*)
----------
       499