关于IN-LIST迭代

IN-list iterator (IN-list迭代)

字段有索引，in里有多少个值就执行多少次索引扫描。不管值是否在字段里存在~
SQL> create table t1 as select * from dba_objects;

表已创建。

SQL> create index idx_object_id on t1(object_id);

索引已创建。

SQL> select count(1) from t1 where object_id=1;

  COUNT(1)
----------
         0
SQL> select object_name,object_id from t1 where object_id in (1,2,3,4,5);

OBJECT_NAME			OBJECT_ID
------------------------------ ----------
I_OBJ#					3
CLU$					5
C_OBJ#					2
TAB$					4

分析表:
BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'HR',
                                tabname          => 't1',
                                estimate_percent => 30,
                                method_opt       => 'for all columns size repeat',
                                no_invalidate    => FALSE,
                                degree           => 8,
                                cascade          => TRUE);
END;

SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------
SQL_ID	97md06hm8ktgp, child number 1
-------------------------------------
select object_name,object_id from t1 where object_id in (1,2,3,4,5)

Plan hash value: 2643144985

--------------------------------------------------------------------------------------------------------
| Id  | Operation		     | Name	     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |		     |	    1 |        |      4 |00:00:00.01 |	    11 |
|   1 |  INLIST ITERATOR	     |		     |	    1 |        |      4 |00:00:00.01 |	    11 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T1	     |	    5 |      5 |      4 |00:00:00.01 |	    11 |
|*  3 |    INDEX RANGE SCAN	     | IDX_OBJECT_ID |	    5 |      5 |      4 |00:00:00.01 |	     9 |
--------------------------------------------------------------------------------------------------------

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

   3 - access(("OBJECT_ID"=1 OR "OBJECT_ID"=2 OR "OBJECT_ID"=3 OR "OBJECT_ID"=4 OR
	      "OBJECT_ID"=5))

21 rows selected.

相当于

SQL> select object_name, object_id
  from t1
 where (("OBJECT_ID" = 1 OR "OBJECT_ID" = 2 OR "OBJECT_ID" = 3 OR
       "OBJECT_ID" = 4 OR "OBJECT_ID" = 5))  2    3    4  ;

SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	gpsm02nfqx6qz, child number 0
-------------------------------------
select object_name, object_id	from t1  where (("OBJECT_ID" = 1 OR
"OBJECT_ID" = 2 OR "OBJECT_ID" = 3 OR	     "OBJECT_ID" = 4 OR
"OBJECT_ID" = 5))

Plan hash value: 2643144985

--------------------------------------------------------------------------------------------------------
| Id  | Operation		     | Name	     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |		     |	    1 |        |      4 |00:00:00.01 |	    11 |
|   1 |  INLIST ITERATOR	     |		     |	    1 |        |      4 |00:00:00.01 |	    11 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T1	     |	    5 |      5 |      4 |00:00:00.01 |	    11 |
|*  3 |    INDEX RANGE SCAN	     | IDX_OBJECT_ID |	    5 |      5 |      4 |00:00:00.01 |	     9 |
--------------------------------------------------------------------------------------------------------

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

   3 - access(("OBJECT_ID"=1 OR "OBJECT_ID"=2 OR "OBJECT_ID"=3 OR "OBJECT_ID"=4 OR
	      "OBJECT_ID"=5))

23 rows selected.