ERROR 1062 (23000): Duplicate entry .....

I have created a table called t as:

Code:

---

CREATE TABLE t (
  name varchar(7) default NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8

---

and inserted following values into it:

Code:

---

insert into t values ('Chagh'),('Ach'),('Achchany');
 commit;

---

now I want to report a numbered list according to alphabetical sort of values,so I issued this SQL:

Code:

---

mysql> select count(t2.name) num,t1.name
    -> from t t1,t t2
    -> where t2.name <= t1.name
    -> group by t1.name
    -> order by num;

---

ERROR 1062 (23000): Duplicate entry 'Chagh' for key 1

I repeat the same scenario in Oracle successfuly.What is the problem in your opinion?
-Thanks in advance