Different access / filter predicate, same plan_hash_value

[oracle@stormking cdb12102 sqlplan]$ sqlplus /nolog @ accessvsfilter.SQL

SQL*Plus: RELEASE 12.1.0.2.0 Production ON Sun Apr 26 13:17:25 2015

Copyright (c) 1982, 2014, Oracle.  ALL rights reserved.

Connected.
SQL> SET linesize 200
SQL> SET pagesize 0
SQL> SET trimspool ON
SQL> WHENEVER oserror EXIT 1
SQL> variable sqlid1 VARCHAR2(13)
SQL> variable cld1 NUMBER
SQL> variable phv1 NUMBER
SQL> variable sqlid2 VARCHAR2(13)
SQL> variable cld2 NUMBER
SQL> variable phv2 NUMBER
SQL> variable xplanopts VARCHAR2(40)
SQL> EXEC :xplanopts := 'basic'

PL/SQL PROCEDURE successfully completed.

SQL> EXEC :xplanopts := NULL

PL/SQL PROCEDURE successfully completed.

SQL>
SQL> DROP TABLE p;

TABLE dropped.

SQL> CREATE TABLE p (
  2  m NUMBER,
  3  n NUMBER,
  4  a NUMBER
  5  );

TABLE created.

SQL> CREATE INDEX i ON p ( m, n );

INDEX created.

SQL> INSERT INTO p ( m, n, a )
  2  SELECT
  3  MOD ( LEVEL, 499979 ),
  4  MOD ( LEVEL, 131 ),
  5  MOD ( LEVEL, 137 )
  6  FROM dual
  7  CONNECT BY LEVEL <=1000000;

1000000 ROWS created.

SQL>
SQL> EXEC dbms_stats.gather_table_stats(NULL,'p' );

PL/SQL PROCEDURE successfully completed.

SQL>
SQL> SELECT m, n, a FROM p WHERE m = 499978 AND n = 34;
    499978         34        131

SQL> @ phv1
SQL> BEGIN
  2  SELECT sql_id, child_number, plan_hash_value INTO :sqlid1, :cld1, :phv1
  3  FROM v$sql
  4  WHERE ( sql_id, child_number ) IN (
  5          SELECT prev_sql_id, prev_child_number
  6          FROM v$session WHERE sid = SYS_CONTEXT( 'userenv','sid' )
  7  );
  8  END;
  9  /

PL/SQL PROCEDURE successfully completed.

SQL> @ xpl1
SQL> SELECT * FROM TABLE( dbms_xplan.display_cursor( :sqlid1, :cld1, :xplanopts ));
SQL_ID  f8x4m8pwykd98, child NUMBER 0
-------------------------------------
SELECT m, n, a FROM p WHERE m = 499978 AND n = 34

PLAN hash VALUE: 1743606228

--------------------------------------------------------------------------------------------
| Id  | Operation                           | Name | ROWS  | Bytes | COST (%CPU)| TIME     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |      |       |       |     4 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| P    |     1 |    11 |     4   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN                  | I    |     1 |       |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------

Predicate Information (IDENTIFIED BY operation id):
---------------------------------------------------

   2 - ACCESS("M"=499978 AND "N"=34)


19 ROWS selected.

SQL>
SQL> DROP INDEX i;

INDEX dropped.

SQL> CREATE INDEX i ON p ( m );

INDEX created.

SQL> SELECT m, n, a FROM p WHERE m = 499978 AND n = 34;
    499978         34        131

SQL> @ phv2
SQL> BEGIN
  2  SELECT sql_id, child_number, plan_hash_value INTO :sqlid2, :cld2, :phv2
  3  FROM v$sql
  4  WHERE ( sql_id, child_number ) IN (
  5          SELECT prev_sql_id, prev_child_number
  6          FROM v$session WHERE sid = SYS_CONTEXT( 'userenv','sid' )
  7  );
  8  END;
  9  /

PL/SQL PROCEDURE successfully completed.

SQL> @ xpl2
SQL> SELECT * FROM TABLE( dbms_xplan.display_cursor( :sqlid2, :cld2, :xplanopts ));
SQL_ID  f8x4m8pwykd98, child NUMBER 0
-------------------------------------
SELECT m, n, a FROM p WHERE m = 499978 AND n = 34

PLAN hash VALUE: 1743606228

--------------------------------------------------------------------------------------------
| Id  | Operation                           | Name | ROWS  | Bytes | COST (%CPU)| TIME     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |      |       |       |     5 (100)|          |
|*  1 |  TABLE ACCESS BY INDEX ROWID BATCHED| P    |     1 |    11 |     5   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN                  | I    |     2 |       |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------

Predicate Information (IDENTIFIED BY operation id):
---------------------------------------------------

   1 - filter("N"=34)
   2 - ACCESS("M"=499978)


20 ROWS selected.

SQL> @ cmp
SQL> SELECT :sqlid1, :cld1, :phv1, :sqlid2, :cld2, :phv2, CASE WHEN :phv1 = :phv2 THEN 'SAME' ELSE 'DIFFERENT' END cmp FROM dual;
f8x4m8pwykd98                             0 1743606228 f8x4m8pwykd98                             0 1743606228 SAME