drop user jon cascade;
grant dba to jon identified by jon;
conn jon/jon

create table emp as select * from scott.emp;
create materialized view mv1 enable query rewrite as
select deptno,sum(sal) from emp group by deptno;

select object_name,object_type from user_objects;
select index_name,column_name from user_ind_columns where table_name='MV1';
select column_name,hidden_column from user_tab_cols where table_name='MV1';

select deptno,"SUM(SAL)",sys_nc00003$ from mv1;

orcl> select * from dual where null=null;

no rows selected

orcl> select * from dual where sys_op_map_nonnull(null)=sys_op_map_nonnull(null);

D
-
X

orcl>