SQL> create table clustered as select rownum a, rownum b, rownum c
   2   from dba_objects ;

SQL> create index clustered_i on clustered (a);

SQL> create table badclustered as select rownum a, rownum b, rownum c
   2   from dba_objects order by dbms_utility.get_hash_value(rownum, 0 , 65536 );

SQL> create index badclustered_i on badclustered (a);

SQL> select index_name, clustering_factor 
   2   from dba_indexes
   3   where owner = 'TEST' and index_name like '%CLUSTER%';

INDEX_NAME                     CLUSTERING_FACTOR
------------------------------ -----------------
BADCLUSTERED_I                              47520 
CLUSTERED_I                                   129 

SQL> select * from clustered where a between  0  and  1500 ;

Execution Plan
----------------------------------------------------------                      
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    TABLE ACCESS (FULL) OF 'CLUSTERED'

Statistics
----------------------------------------------------------                      
         233   consistent gets                                                    
        1500   rows processed                                                     

SQL> select * from clustered where a between  0  and  1200 ;

Execution Plan
----------------------------------------------------------                      
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    TABLE ACCESS (BY INDEX ROWID) OF 'CLUSTERED' 
    2      1      INDEX (RANGE SCAN) OF 'CLUSTERED_I' (NON-UNIQUE)

Statistics
----------------------------------------------------------                      
         167   consistent gets                                                    
        1200   rows processed                                                     

SQL> select * from badclustered where a between  0  and  5 ;

Execution Plan
----------------------------------------------------------                      
    0       SELECT STATEMENT Optimizer=CHOOSE 
    1      0    TABLE ACCESS (BY INDEX ROWID) OF 'BADCLUSTERED'  
    2      1      INDEX (RANGE SCAN) OF 'BADCLUSTERED_I' (NON-UNIQUE)

Statistics
----------------------------------------------------------                      
           8   consistent gets                                                    
           5   rows processed                                                     

SQL> select * from badclustered where a between  0  and  8 ;

Execution Plan
----------------------------------------------------------                      
    0       SELECT STATEMENT Optimizer=CHOOSE  
    1      0    TABLE ACCESS (FULL) OF 'BADCLUSTERED' 

Statistics
----------------------------------------------------------                      
         134   consistent gets                                                    
           8   rows processed                                                     

SQL> drop index badclustered_i;

SQL> create unique index badclustered_i2 on badclustered (a);

SQL> select * from badclustered where a between  0  and  8 ;

Execution Plan
----------------------------------------------------------                      
    0       SELECT STATEMENT Optimizer=CHOOSE  
    1      0    TABLE ACCESS (FULL) OF 'BADCLUSTERED'              
                                                                                
Statistics
----------------------------------------------------------                      
         134   consistent gets                                                    
           8   rows processed                                                     

SQL> select * from badclustered where a between  0  and  5 ;

Execution Plan
----------------------------------------------------------                      
    0       SELECT STATEMENT Optimizer=CHOOSE 
    1      0    TABLE ACCESS (BY INDEX ROWID) OF 'BADCLUSTERED' 
    2      1      INDEX (RANGE SCAN) OF 'BADCLUSTERED_I2' (UNIQUE)

Statistics
----------------------------------------------------------                      
           8   consistent gets                                                    
           5   rows processed