SQL> create table t1
  2  (x number, txt varchar2(30));

Table created.

SQL> create table t2(x number, txt varchar2(30));

Table created.

SQL> insert into t1 select rownum, owner from all_objects
  2  ;

29129 rows created.

SQL> insert into t2 select rownum, owner from all_objects
  2  where rownum<3000;

2999 rows created.

SQL> insert into t2 select * from t2;

2999 rows created.

SQL> /

5998 rows created.

SQL> /

11996 rows created.

SQL> /

23992 rows created.

SQL> commit;

this bit is just ensuring that we have approximately the same records in both tables
Commit complete.

SQL> select count(*)-29129 from t2;

COUNT(*)-29129
--------------
         18855

SQL> delete from t2 where rownum<=18854;

18854 rows deleted.

SQL> create index t1idx on t1(x);

Index created.

SQL> create index t2idx on t2(x);

Index created.

SQL> analyze table t1 compute statistics;

Table analyzed.

SQL> analyze table t2 compute statistics;

Table analyzed.

SQL> set autotrace traceonly;
SQL> select * from t1 where x =2;


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=9)
   1    0   TABLE ACCESS (BY INDEX ROWID) OF 'T1' (Cost=2 Card=1 Bytes
          =9)

   2    1     INDEX (RANGE SCAN) OF 'T1IDX' (NON-UNIQUE) (Cost=1 Card=
          1)


SQL> select * from t2 where x =2;

9 rows selected.


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=10 Card=10 Bytes=60)
   1    0   TABLE ACCESS (FULL) OF 'T2' (Cost=10 Card=10 Bytes=60)