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.