BEGIN
   DBMS_RLS.ADD_POLICY (object_schema           => 'USER1',
                        object_name             => 'tde_test',
                        policy_name             => 'test_vpd',
                        function_schema         => 'USER1',
                        policy_function         => 'vpd_function',
                        sec_relevant_cols       => 'COL1',
                        sec_relevant_cols_opt   => DBMS_RLS.ALL_ROWS);
END;
/

CREATE OR REPLACE FUNCTION vpd_function (obj_owner   IN VARCHAR2,
                                         obj_name    IN VARCHAR2)
   RETURN VARCHAR2
AS
BEGIN
    IF SYS_CONTEXT ('USERENV', 'SESSION_USER')  IN ('USER1','USER2')
	THEN  
	    RETURN '1=2';
	ELSE
        RETURN NULL;
    END IF;
END;
/

SQL> create table t as
  2  select level id, to_char(to_date(level,'J'),'fmjsp') val from dual connect by level <= 10
  3  /

Table created.

SQL> select * from t order by id;
        ID VAL
---------- ------------------------------------------------------------------------------
         1 one
         2 two
         3 three
         4 four
         5 five
         6 six
         7 seven
         8 eight
         9 nine
        10 ten

10 rows selected.

SQL> BEGIN
  2     DBMS_RLS.ADD_POLICY (object_schema           => 'MICHEL',
  3                          object_name             => 'T',
  4                          policy_name             => 'T_VPD',
  5                          function_schema         => 'MICHEL',
  6                          policy_function         => 'T_VPD_FUNCTION',
  7                          sec_relevant_cols       => 'VAL',
  8                          sec_relevant_cols_opt   => DBMS_RLS.ALL_ROWS);
  9  END;
 10  /

PL/SQL procedure successfully completed.

SQL> CREATE OR REPLACE FUNCTION T_VPD_FUNCTION (obj_owner   IN VARCHAR2,
  2                                             obj_name    IN VARCHAR2)
  3     RETURN VARCHAR2
  4  AS
  5  BEGIN
  6      IF SYS_CONTEXT ('USERENV', 'SESSION_USER')  IN ('USER1','USER2')
  7     THEN
  8         RETURN '1=2';
  9     ELSE
 10          RETURN NULL;
 11      END IF;
 12  END;
 13  /

Function created.

SQL> create user user1 identified by user1;

User created.

SQL> grant create session to user1;

Grant succeeded.

SQL> grant select on t to user1;

Grant succeeded.

SQL> connect user1/user1
Connected.
USER1> select * from michel.t order by id;
        ID V
---------- -
         1
         2
         3
         4
         5
         6
         7
         8
         9
        10

10 rows selected.

IF SYS_CONTEXT ('USERENV', 'SESSION_USER')  IN ('SYS')
	THEN  
	    RETURN '1=2';
	ELSE
        RETURN NULL;
    END IF;