通常我们使用hint来固定查询计划选择走表的索引 固定表的连接等等，但是如果第一层查询的是视图呢？
yang@rac1>CREATE TABLE TA (ID NUMBER, NAME VARCHAR2(30), TYPE VARCHAR2(30));
Table created.
yang@rac1>CREATE TABLE TB (ID NUMBER, NAME VARCHAR2(30), TYPE VARCHAR2(30));
Table created.
yang@rac1>create index idx_id_ta on ta(id);
Index created.
yang@rac1>create index idx_id_tb on tb(id);
Index created.
yang@rac1>CREATE VIEW V_Tab AS
2 SELECT * FROM TA
3 UNION ALL
4 SELECT * FROM TB;
View created.
普通的查询视图，并没有走索引。
yang@rac1> SELECT *
2 FROM V_TAB
3 WHERE ID<2500;
9996 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 4036260501
-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 2 (0)| 00:00:01 |
| 1 | VIEW | V_TAB | 1 | 47 | 2 (0)| 00:00:01 |
| 2 | UNION-ALL | | | | | |
|* 3 | TABLE ACCESS FULL| TA | 4998 | 229K| 9 (0)| 00:00:01 |
|* 4 | TABLE ACCESS FULL| TB | 4998 | 229K| 9 (0)| 00:00:01 |
-----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("ID"<2500)
4 - filter("ID"<2500)
Note
-----
- dynamic sampling used for this statement (level=2)
====使用常规使用hint的方式(表名 索引名称)
yang@rac1> SELECT /*+ index(tb idx_id_tb) index(ta idx_id_ta) */*
2 FROM V_TAB
3 WHERE ID<2500;
9996 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 4036260501
-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 2 (0)| 00:00:01 |
| 1 | VIEW | V_TAB | 1 | 47 | 2 (0)| 00:00:01 |
| 2 | UNION-ALL | | | | | |
|* 3 | TABLE ACCESS FULL| TA | 4998 | 229K| 9 (0)| 00:00:01 |
|* 4 | TABLE ACCESS FULL| TB | 4998 | 229K| 9 (0)| 00:00:01 |
-----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("ID"<2500)
4 - filter("ID"<2500)
并不凑效！依然走全表扫描！
Note
-----
- dynamic sampling used for this statement (level=2)
==使用 视图前缀修饰表名的方式(VIVE.TABNAME INDEX_NAME)
yang@rac1> SELECT /*+ index(v_tab.tb idx_id_tb) index(v_tab.ta idx_id_ta) */*
2 FROM V_TAB
3 WHERE ID<2500;
9996 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 531820221
-------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 2 (0)| 00:00:01 |
| 1 | VIEW | V_TAB | 1 | 47 | 2 (0)| 00:00:01 |
| 2 | UNION-ALL | | | | | |
| 3 | TABLE ACCESS BY INDEX ROWID| TA | 4998 | 229K| 18 (0)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | IDX_ID_TA | 4998 | | 18 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID| TB | 4998 | 229K| 5016 (1)| 00:01:01 |
|* 6 | INDEX RANGE SCAN | IDX_ID_TB | 4998 | | 17 (0)| 00:00:01 |
-------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("ID"<2500)
6 - access("ID"<2500)
yang@rac1>
对于创建视图的时候包含表的别名的情况：
yang@rac1>CREATE VIEW V_Tab02 AS
2 SELECT * FROM TA t1
3 UNION ALL
4 SELECT * FROM TB t2 ;
View created.
yang@rac1> SELECT /*+ index(tb idx_id_tb) index(ta idx_id) */*
2 FROM V_TAB02
3 WHERE ID<2500;
9996 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 3023640653
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 2 (0)| 00:00:01 |
| 1 | VIEW | V_TAB02 | 1 | 47 | 2 (0)| 00:00:01 |
| 2 | UNION-ALL | | | | | |
|* 3 | TABLE ACCESS FULL| TA | 4998 | 229K| 9 (0)| 00:00:01 |
|* 4 | TABLE ACCESS FULL| TB | 4998 | 229K| 9 (0)| 00:00:01 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("ID"<2500)
4 - filter("ID"<2500)
yang@rac1> SELECT /*+ index(v_tab02.tb idx_id_tb) index(v_tab02.ta idx_id) */*
2 FROM V_TAB02
3 WHERE ID<2500;
9996 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 3023640653
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 2 (0)| 00:00:01 |
| 1 | VIEW | V_TAB02 | 1 | 47 | 2 (0)| 00:00:01 |
| 2 | UNION-ALL | | | | | |
|* 3 | TABLE ACCESS FULL| TA | 4998 | 229K| 9 (0)| 00:00:01 |
|* 4 | TABLE ACCESS FULL| TB | 4998 | 229K| 9 (0)| 00:00:01 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("ID"<2500)
4 - filter("ID"<2500)
==此时必须使用创建视图的表的相对应的别名(VIVE.TAB_ALIAS_NAME INDEX_NAME)
yang@rac1> SELECT /*+ index(v_tab02.t2 idx_id_tb) index(v_tab02.t1 idx_id) */*
2 FROM V_TAB02
3 WHERE ID<2500;
9996 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 3173198873
-------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 47 | 2 (0)| 00:00:01 |
| 1 | VIEW | V_TAB02 | 1 | 47 | 2 (0)| 00:00:01 |
| 2 | UNION-ALL | | | | | |
| 3 | TABLE ACCESS BY INDEX ROWID| TA | 4998 | 229K| 18 (0)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | IDX_ID | 4998 | | 18 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID| TB | 4998 | 229K| 5016 (1)| 00:01:01 |
|* 6 | INDEX RANGE SCAN | IDX_ID_TB | 4998 | | 17 (0)| 00:00:01 |
-------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("ID"<2500)
6 - access("ID"<2500)
Note
-----
- dynamic sampling used for this statement (level=2)
