如何利用oracle 10g的列值掩码技术隐藏敏感数据

BEGIN
     DBMS_RLS.ADD_POLICY(object_schema=>'HR',
                         object_name=>'EMPLOYEES',
                         policy_name=>'restrict_dept_policy',
                         function_schema=>'HR',
                         policy_function=>'rls_dept',
                         sec_relevant_cols=>'salary,commission_pct',
                         sec_relevant_cols_opt=>dbms_rls.ALL_ROWS);
END;
/