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:
BEGINDBMS_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
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SQL_ID 97md06hm8ktgp, child number 1
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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_idfrom t1where (("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
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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.