我有一个视图，我想像这样查询我的视图以提示基表中的一些索引，我可以这样做吗？
我是说：
--view
create or replace view temp_view
as select col1,col2,col3
from table1,table2....
我在table1.col1上有一个名为“ index1 ”的索引。
我有一个查询：
--query
select *
from temp_view
where col1=12;
当我看到这个查询的解释计划时，它告诉我查询不使用“index1”，我想指出它..
所以我希望它是，例如：
--query with hint
select /*+ index(temp_view index1)*/*
from temp_view
where col1=12;
我可以指出意见的提示吗？（如果我不想在创建此视图期间指出它）
您可以在针对视图的查询中使用提示来强制 Oracle 使用基表上的索引。但是您需要知道基础视图中基表的别名（如果有）。一般语法是/*+ index(<<alias of view from query>> <<alias of table from view>> <<index name>>) */
一个例子
1) 创建一个包含 10,000 个相同行的表，并在该表上创建索引。索引没有选择性，所以 Oracle 不想使用它
SQL> ed
Wrote file afiedt.buf
1 create table foo
2 as
3 select 1 col1
4 from dual
5* connect by level <= 10000
SQL> /
Table created.
SQL> create index idx_foo on foo(col1);
Index created.
2) 验证索引没有正常使用但是Oracle会提示使用
SQL> set autotrace traceonly;
SQL> select * from foo where col1 = 1;
10000 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1245013993
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 10000 | 126K| 7 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| FOO | 10000 | 126K| 7 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("COL1"=1)
Note
-----
- dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
9 recursive calls
0 db block gets
713 consistent gets
5 physical reads
0 redo size
172444 bytes sent via SQL*Net to client
7849 bytes received via SQL*Net from client
668 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
10000 rows processed
SQL> select /*+ index(foo idx_foo) */ *
2 from foo
3 where col1 = 1;
10000 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 15880034
----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 10000 | 126K| 25 (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| IDX_FOO | 10000 | 126K| 25 (0)| 00:00:01 |
----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("COL1"=1)
Note
-----
- dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
7 recursive calls
0 db block gets
715 consistent gets
15 physical reads
0 redo size
172444 bytes sent via SQL*Net to client
7849 bytes received via SQL*Net from client
668 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
10000 rows processed
3) 现在创建视图。通过指定查询中的视图别名和视图定义中的表别名来验证针对视图的正常查询不使用索引，而是强制使用索引
SQL> create view vw_foo
2 as
3 select col1
4 from foo f;
View created.
SQL> select col1
2 from vw_foo
3 where col1 = 1;
10000 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1245013993
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 10000 | 126K| 7 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| FOO | 10000 | 126K| 7 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("COL1"=1)
Note
-----
- dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
16 recursive calls
0 db block gets
715 consistent gets
0 physical reads
0 redo size
172444 bytes sent via SQL*Net to client
7849 bytes received via SQL*Net from client
668 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
10000 rows processed
SQL> select /*+ index(vf f idx_foo) */ col1
2 from vw_foo vf
3 where col1 = 1;
10000 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 15880034
----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 10000 | 126K| 25 (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| IDX_FOO | 10000 | 126K| 25 (0)| 00:00:01 |
----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("COL1"=1)
Note
-----
- dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
14 recursive calls
0 db block gets
717 consistent gets
0 physical reads
0 redo size
172444 bytes sent via SQL*Net to client
7849 bytes received via SQL*Net from client
668 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
10000 rows processed
SQL>
尽管如此，在尝试调整查询时，提示通常是最后的手段——通常最好找出优化器缺少哪些信息并提供适当的统计信息，以便它可以自己做出正确的选择。这是一个更稳定的解决方案。更重要的是，当您减少到指定涉及多层别名的提示时 - 例如，触摸视图定义的人很容易通过更改表名的别名来破坏您的查询。
我尝试了 Justin Cave 的（旁边的答案）语法
select /*+ index(vf f idx_foo) */ col1
from vw_foo vf
where col1 = 1;
，但它对我不起作用。下一个工作
select /*+ index(vf.f idx_foo) */ col1
from vw_foo vf
where col1 = 1;
我在Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production上试过