in-list iterator

in-list iterator

--針對目標sql的in後面是常量集合的首選項處理方法，其處理效率一般都會比in-list expansion高
--使用in-list iterator的時候，in所在列上必定要有索引
--能夠經過聯合設置10142和10157事件來禁掉in-list iterator，可是沒有hint來強制使用in-list iterator

SQL> create table emp1 as select * from emp;
SQL> create index idx_emp1_dept on emp1(deptno);
SQL> select * from emp1 where deptno in (10,20,30);
SQL> select * from table(dbms_xplan.display_cursor(null,null,'advanced'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------
SQL_ID  df7dw3ph8g0t7, child number 0
-------------------------------------
select * from emp1 where deptno in (10,20,30)

Plan hash value: 2544692611

----------------------------------------------------------------------------------------------
| Id  | Operation                    | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |               |       |       |     2 (100)|          |
|   1 |  INLIST ITERATOR             |               |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| EMP1          |    14 |  1218 |     2   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN          | IDX_EMP1_DEPT |     1 |       |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------

oracle中in和or是等價的：

SQL> select * from emp1 where deptno=10 or deptno=20 or deptno=30;
SQL> select * from table(dbms_xplan.display_cursor(null,null,'advanced'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------
SQL_ID  2yya3cuswm15m, child number 0
-------------------------------------
select * from emp1 where deptno=10 or deptno=20 or deptno=30

Plan hash value: 2544692611

----------------------------------------------------------------------------------------------
| Id  | Operation                    | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |               |       |       |     2 (100)|          |
|   1 |  INLIST ITERATOR             |               |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| EMP1          |    14 |  1218 |     2   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN          | IDX_EMP1_DEPT |     1 |       |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------

　　

刪除索引後就會走全表掃描，用不到INLIST ITERATOR的：

SQL> drop index idx_emp1_dept;
SQL> select * from emp1 where deptno in (10,20,30);
SQL> select * from table(dbms_xplan.display_cursor(null,null,'advanced'));

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
SQL_ID  df7dw3ph8g0t7, child number 0
-------------------------------------
select * from emp1 where deptno in (10,20,30)

Plan hash value: 2226897347

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |     3 (100)|          |
|*  1 |  TABLE ACCESS FULL| EMP1 |    14 |  1218 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

　　

 使用in-list iterator優化示例：http://blog.csdn.net/zengxuewen2045/article/details/52017297