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)---------- 0SQL> select object_name,object_id from t1 where object_id in (1,2,3,4,5);OBJECT_NAME OBJECT_ID------------------------------ ----------I_OBJ# 3CLU$ 5C_OBJ# 2TAB$ 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.