and_equal,index_join,index_combine
and_equal,index_join,index_combine这三种都是oracle利用索引关联获得数据的方法,三者的目的都是为了最大限度的利用索引,减少回表的代价.但是三者的实现方法是有区别的,下面一一来分析.
and_equal:
这种方式需要查询条件里面包括所有索引列,然后取得每个索引中得到的rowid列表,然后对这些列表做merge join,过滤出相同的rowid后再去表中获取数据或者直接从索引中获得数据.and_equal有一些限制,比如它只对单列索引有效,只对非唯一索引有效,使用到的索引不能超过5个,查询条件只能是"=".在10g中,and_equal已经被废弃了,只能通过hint才能生效.
这种方式需要查询条件里面包括所有索引列,然后取得每个索引中得到的rowid列表,然后对这些列表做merge join,过滤出相同的rowid后再去表中获取数据或者直接从索引中获得数据.and_equal有一些限制,比如它只对单列索引有效,只对非唯一索引有效,使用到的索引不能超过5个,查询条件只能是"=".在10g中,and_equal已经被废弃了,只能通过hint才能生效.
create table test as select * from dba_objects;
create index ind_test_owner on test(owner);
create index ind_test_object_name on test(object_name);
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name from test where owner='test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
|* 1 | AND-EQUAL | | | | |
|* 2 | INDEX RANGE SCAN| IND_TEST_OWNER | 1 | | 1 (0)|
|* 3 | INDEX RANGE SCAN| IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
|* 1 | AND-EQUAL | | | | |
|* 2 | INDEX RANGE SCAN| IND_TEST_OWNER | 1 | | 1 (0)|
|* 3 | INDEX RANGE SCAN| IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-------------------------------------------------------------------------------
如果查询条件只包含owner
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name from test where owner='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 29 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 29 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
-----------------------------------------------------------------------------------
修改owner,object_name为非空
alter table test modify(owner not null);
alter table test modify(object_name not null);
alter table test modify(object_name not null);
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name from test where owner='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 29 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 29 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
-----------------------------------------------------------------------------------
效果一样
查询条件是">"的情况
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name,object_type from test where owner>'test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-----------------------------------------------------------------------------------------
查询条件是in的情况
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name,object_type from test where owner in('test','dba') and object_name='test';
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name,object_type from test where owner in('test','dba') and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-----------------------------------------------------------------------------------------
再来看一下回表的情况
SQL 10G>select/*+ and_equal(test ind_test_owner ind_test_object_name)*/ owner,object_name,object_type from test where owner='test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
| 2 | AND-EQUAL | | | | |
|* 3 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
|* 4 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
| 2 | AND-EQUAL | | | | |
|* 3 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
|* 4 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | 2 | | 1 (0)|
-----------------------------------------------------------------------------------------
先通过and_equal取得rowid列表,然后从表中返回数据.
index_join:
index join顾名思义是对index进行关联,oracle通过hash index join的方式实现了避免对表的访问.所有的数据都从索引中直接获得.它不受查询条件影响,可以是唯一索引,也可以是多列索引.
index join顾名思义是对index进行关联,oracle通过hash index join的方式实现了避免对表的访问.所有的数据都从索引中直接获得.它不受查询条件影响,可以是唯一索引,也可以是多列索引.
SQL 10G>select/*+ index_join(test ind_test_owner ind_test_object_name)*/ owner,object_name from test where owner='test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
--------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 3 (34)|
|* 1 | VIEW | index$_join$_001 | 1 | 29 | 3 (34)|
|* 2 | HASH JOIN | | | | |
|* 3 | INDEX RANGE SCAN| IND_TEST_OWNER | 1 | 29 | 1 (0)|
|* 4 | INDEX RANGE SCAN| IND_TEST_OBJECT_NAME | 1 | 29 | 1 (0)|
--------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 3 (34)|
|* 1 | VIEW | index$_join$_001 | 1 | 29 | 3 (34)|
|* 2 | HASH JOIN | | | | |
|* 3 | INDEX RANGE SCAN| IND_TEST_OWNER | 1 | 29 | 1 (0)|
|* 4 | INDEX RANGE SCAN| IND_TEST_OBJECT_NAME | 1 | 29 | 1 (0)|
--------------------------------------------------------------------------------
可以不带查询条件,只不过由index range scan变成了index fast full scan
SQL 10G>select/*+ index_join(test ind_test_owner ind_test_object_name)*/ owner,object_name from test
2 ;
2 ;
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 51984 | 1472K| 478 (2)|
| 1 | VIEW | index$_join$_001 | 51984 | 1472K| 478 (2)|
|* 2 | HASH JOIN | | | | |
| 3 | INDEX FAST FULL SCAN| IND_TEST_OWNER | 51984 | 1472K| 153 (2)|
| 4 | INDEX FAST FULL SCAN| IND_TEST_OBJECT_NAME | 51984 | 1472K| 322 (1)|
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 51984 | 1472K| 478 (2)|
| 1 | VIEW | index$_join$_001 | 51984 | 1472K| 478 (2)|
|* 2 | HASH JOIN | | | | |
| 3 | INDEX FAST FULL SCAN| IND_TEST_OWNER | 51984 | 1472K| 153 (2)|
| 4 | INDEX FAST FULL SCAN| IND_TEST_OBJECT_NAME | 51984 | 1472K| 322 (1)|
------------------------------------------------------------------------------------
如果不是所有数据都能从索引获得,那么将不会使用index join
SQL 10G>select/*+ index_join(test ind_test_owner ind_test_object_name)*/ owner,object_name,object_type from test where owner='test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 40 | 2 (0)|
|* 2 | INDEX RANGE SCAN | IND_TEST_OWNER | 1 | | 1 (0)|
-----------------------------------------------------------------------------------
index_combine:
index combine最早是用在bitmap index上的,在9i开始oracle默认可以使用在btree索引上,这是由_b_tree_bitmap_plans参数来控制的.oracle将btree索引中获得的rowid信息通过BITMAP CONVERSION FROM ROWIDS的步骤转换成bitmap进行匹配,然后匹配完成后通过BITMAP CONVERSION TO ROWIDS再转换出rowid获得数据或者回表获得数据.
SQL 10G>select/*+ index_combine(test ind_test_owner ind_test_object_name)*/ owner,object_name from test where owner='test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
| 1 | BITMAP CONVERSION TO ROWIDS | | 1 | 29 | 2 (0)|
| 2 | BITMAP AND | | | | |
| 3 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 4 | INDEX RANGE SCAN | IND_TEST_OWNER | | | 1 (0)|
| 5 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 6 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | | | 1 (0)|
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 2 (0)|
| 1 | BITMAP CONVERSION TO ROWIDS | | 1 | 29 | 2 (0)|
| 2 | BITMAP AND | | | | |
| 3 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 4 | INDEX RANGE SCAN | IND_TEST_OWNER | | | 1 (0)|
| 5 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 6 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | | | 1 (0)|
---------------------------------------------------------------------------------------------
回表取数据的情况
SQL 10G>select/*+ index_combine(test ind_test_owner ind_test_object_name)*/ owner,object_name,object_type from test where owner='test' and object_name='test';
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID | TEST | 1 | 40 | 2 (0)|
| 2 | BITMAP CONVERSION TO ROWIDS | | | | |
| 3 | BITMAP AND | | | | |
| 4 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 5 | INDEX RANGE SCAN | IND_TEST_OWNER | | | 1 (0)|
| 6 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 7 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | | | 1 (0)|
----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 40 | 2 (0)|
| 1 | TABLE ACCESS BY INDEX ROWID | TEST | 1 | 40 | 2 (0)|
| 2 | BITMAP CONVERSION TO ROWIDS | | | | |
| 3 | BITMAP AND | | | | |
| 4 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 5 | INDEX RANGE SCAN | IND_TEST_OWNER | | | 1 (0)|
| 6 | BITMAP CONVERSION FROM ROWIDS| | | | |
|* 7 | INDEX RANGE SCAN | IND_TEST_OBJECT_NAME | | | 1 (0)|
----------------------------------------------------------------------------------------------
不带查询条件的情况,index combine将不被使用
SQL 10G>select/*+ index_combine(test ind_test_owner ind_test_object_name)*/ owner,object_name from test
2 ;
2 ;
Execution Plan
----------------------------------------------------------
----------------------------------------------------------
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 51984 | 1472K| 1480 (1)|
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 51984 | 1472K| 1480 (1)|
| 2 | INDEX FULL SCAN | IND_TEST_OWNER | 51984 | | 123 (2)|
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 51984 | 1472K| 1480 (1)|
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 51984 | 1472K| 1480 (1)|
| 2 | INDEX FULL SCAN | IND_TEST_OWNER | 51984 | | 123 (2)|
-----------------------------------------------------------------------------------
index_combine会是and_equal的很好的替代者,随着and_equal的退出,index_combine将更多得被我们看到.
