drop table t purge;
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create table t as select * from dba_objects;
update t set object_id=rownum ;
create index idx_id_type on t(object_id,object_type);
UPDATE t SET OBJECT_ID=20 WHERE ROWNUM<=26000;
UPDATE t SET OBJECT_ID=21 WHERE OBJECT_ID<>20;
COMMIT;
set linesize 1000
set pagesize 1
alter session set statistics_level=all ;
select /*+index(t,idx1_object_id)*/ * from t where object_TYPE='TABLE' AND OBJECT_ID >= 20 AND OBJECT_ID<= 21;
select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
--------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2939 |00:00:00.02 | 1117 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 3411 | 2939 |00:00:00.02 | 1117 |
|* 2 | INDEX RANGE SCAN | IDX_ID_TYPE | 1 | 299 | 2939 |00:00:00.02 | 736 |
--------------------------------------------------------------------------------------------------------
2 - access("OBJECT_ID">=20 AND "OBJECT_TYPE"='TABLE' AND "OBJECT_ID"<=21)
filter("OBJECT_TYPE"='TABLE')
已选择25行。
select /*+index(t,idx_id_type)*/ * from t t where object_TYPE='TABLE' AND OBJECT_ID IN (20,21);
select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
---------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2939 |00:00:00.01 | 598 |
| 1 | INLIST ITERATOR | | 1 | | 2939 |00:00:00.01 | 598 |
| 2 | TABLE ACCESS BY INDEX ROWID| T | 2 | 3411 | 2939 |00:00:00.01 | 598 |
|* 3 | INDEX RANGE SCAN | IDX_ID_TYPE | 2 | 1 | 2939 |00:00:00.01 | 217 |
---------------------------------------------------------------------------------------------------------
3 - access((("OBJECT_ID"=20 OR "OBJECT_ID"=21)) AND "OBJECT_TYPE"='TABLE')
已选择25行。
---col1,col2,col3的索引情况，如果没有为COL2赋予查询条件时，COL3只能起到检验作用(依然是in的优化）
drop table t purge;
create table t as select * from dba_objects;
UPDATE t SET OBJECT_ID=20 WHERE ROWNUM<=26000;
UPDATE t SET OBJECT_ID=21 WHERE OBJECT_ID<>20;
Update t set object_id=22 where rownum<=10000;
COMMIT;
create index idx_union on t(object_type,object_id,owner);
set autotrace off
alter session set statistics_level=all ;
set linesize 1000
select * from t where object_type='VIEW' and OWNER='LJB';
select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |
------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 24 | 19 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 9 | 4 |00:00:00.01 | 24 | 19 |
|* 2 | INDEX RANGE SCAN | IDX_UNION | 1 | 22 | 4 |00:00:00.01 | 21 | 19 |
------------------------------------------------------------------------------------------------------------
select /*+INDEX(T,idx_union)*/ * from t T where object_type='VIEW' and OBJECT_ID IN (20,21,22) AND OWNER='LJB';
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 13 |
| 1 | INLIST ITERATOR | | 1 | | 4 |00:00:00.01 | 13 |
| 2 | TABLE ACCESS BY INDEX ROWID| T | 3 | 1 | 4 |00:00:00.01 | 13 |
|* 3 | INDEX RANGE SCAN | IDX_UNION | 3 | 1 | 4 |00:00:00.01 | 10 |
----------------------------------------------------------------------------------------------------
类似
select /*+INDEX(T,idx_union)*/ * from t T where (object_type='VIEW' and OBJECT_ID =20 AND OWNER='LJB')
or (object_type='VIEW' and OBJECT_ID =21 AND OWNER='LJB')
or (object_type='VIEW' and OBJECT_ID =22 AND OWNER='LJB')