INDEX RANG SCAN无需回表的情况

create table a3 as select * from dba_objects

create index a3_idx1 on a3(owner);

select owner from a3 where owner='SCOTT';

SQL> set linesize 200
SQL> set pagesize 200
SQL> set autot trace
SQL> select owner from a3 where owner='SCOTT';

1870 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 3836947260

----------------------------------------------------------------------------
| Id  | Operation	 | Name    | Rows  | Bytes | Cost (%CPU)| Time	   |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |	   |  1870 | 31790 |	 5   (0)| 00:00:01 |
|*  1 |  INDEX RANGE SCAN| A3_IDX1 |  1870 | 31790 |	 5   (0)| 00:00:01 |
----------------------------------------------------------------------------

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

   1 - access("OWNER"='SCOTT')

Note
-----
   - dynamic sampling used for this statement (level=2)

Statistics
----------------------------------------------------------
	  7  recursive calls
	  0  db block gets
	212  consistent gets
	  0  physical reads
	  0  redo size
      25551  bytes sent via SQL*Net to client
       1783  bytes received via SQL*Net from client
	126  SQL*Net roundtrips to/from client
	  0  sorts (memory)
	  0  sorts (disk)
       1870  rows processed