测试oracle索引回表读开销大

索引组织表IOT表的数据是以已经按主键字段排好序后存放在B-tree索引中的，而堆表的数据则是无序的存放在表段的数据块中。
#############索引回表读开销大
索引组织表

(1)建立表
//建立普通的表
create table heap_add(empno number(10),addr_type varchar2(10),street varchar(10),city varchar2(10),state varchar2(10),primary key(empno));


//索引组织表
create table iot_add(empno number(10),addr_type varchar2(10),street vrchar(10),city varchar2(10),state varchar2(10),primary key(empno)) organizationindex;

(2)插入数据
//普通表插入数据
insert into heap_add select object_id,'teah','louyang','henan,cn',44 from all_objects;
//索引组织表插入数据
insert into iot_add select object_id,'teah','louyang','henan,cn',44 from all_objects;
//必定要commit
commit;

(3)开启执行计划
set autotrace traceonly;

(4)查询一下
普通表：
LISN@orcl>select * from heap_add where empno=22;
select * from heap_add where empno=22;

Execution Plan
----------------------------------------------------------
Plan hash value: 3026474701

--------------------------------------------------------------------------------------------
| Id  | Operation            | Name       | Rows  | Bytes | Cost (%CPU)| Time       |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT        |           |     1 |    41 |     1   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| HEAP_ADD       |     1 |    41 |     1   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN        | SYS_C0011151 |     1 |       |     1   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------

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

   2 - access("EMPNO"=22)


Statistics
----------------------------------------------------------
      1  recursive calls
      0  db block gets
      3  consistent gets
      0  physical reads
      0  redo size
    688  bytes sent via SQL*Net to client
    512  bytes received via SQL*Net from client
      1  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

索引组织表：
LISN@orcl>select * from iot_add where empno=22;
select * from iot_add where empno=22;


Execution Plan
----------------------------------------------------------
Plan hash value: 2557813697

---------------------------------------------------------------------------------------
| Id  | Operation      | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |              |     1 |    41 |     1    (0)| 00:00:01 |
|*  1 |  INDEX UNIQUE SCAN| SYS_IOT_TOP_74712 |     1 |    41 |     1    (0)| 00:00:01 |
---------------------------------------------------------------------------------------

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

   1 - access("EMPNO"=22)


Statistics
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      2  consistent gets
      0  physical reads
      0  redo size
    820  bytes sent via SQL*Net to client
    523  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed