SQL> create table t as select username,password from dba_users;

Table created.

SQL> create index i_t on t(username);

Index created.

SQL> set autotrace trace explain

SQL> select /*+ index(t i_t) */ * from t where username='EYGLE';

Execution Plan
----------------------------------------------------------
Plan hash value: 2928007915

------------------------------------------------------------------------------------
| Id  | Operation                   | Name | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |      |     1 |    34 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T    |     1 |    34 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | I_T  |     1 |       |     1   (0)| 00:00:01 |
------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("USERNAME"='EYGLE')

Note
-----
   - dynamic sampling used for this statement 

SQL> desc t
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 USERNAME                                  NOT NULL VARCHAR2(30)
 PASSWORD                                           VARCHAR2(30)