ORA-32638: Non unique addressing in MODEL dimensions

create table tq84_tab (
   dim_1  number,
   dim_2  varchar2(10),
   val_1  number,
   val_2  number
);

insert into tq84_tab values (1, 'aaa', 17,  9);
insert into tq84_tab values (1, 'bbb', 12,  7);
insert into tq84_tab values (1, 'ccc',  4, 12);
insert into tq84_tab values (2, 'aaa',  2,  6);

insert into tq84_tab values (1, 'bbb', 12,  7);

select * from tq84_tab
model
   dimension by (dim_1, dim_2)
   measures     (val_1, val_2)
   rules        (            )
;

drop table tq84_tab;