默认情况下，Oracle使用创建的索引。

当我更改为NLS_COMP =语言并且NLS_Sort = Binary_CI时，我得到了全表扫描。

我读过某处使用（nlssort（name，’NLS_SORT = BINARY_CI’））创建索引的地方; 会工作。

正如我下面的尝试所示，没有那么多。即使我强行执行，性能似乎也不是我所期望的。这是一个微不足道的示例，我想为具有数百万行的表解决此问题，因此全表扫描将很糟糕。

所以问题是如何建立索引以便使用索引。

谢谢

-设置X

create table x ( name varchar2(30)) ;
insert into x select table_name from all_tables;
create index x_ix on x (name);
create index x_ic on x (nlssort(name, 'NLS_SORT=BINARY_CI'));
/   

• 默认设置

ALTER SESSION SET NLS_COMP=BINARY;
ALTER SESSION SET NLS_SORT=BINARY; 
/
set autotrace on 
/
select * from X where NAME like 'x%';

--0 rows selected
--
---------------------------------------------------------------------------
--| Id  | Operation        | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
--|   0 | SELECT STATEMENT |      |     1 |    17 |     1   (0)| 00:00:01 |
--|*  1 |  INDEX RANGE SCAN| X_IX |     1 |    17 |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------
/
set autotrace off
/

-语言

ALTER SESSION SET NLS_COMP=LINGUISTIC; 
ALTER SESSION SET NLS_SORT=BINARY_CI; 
/
set autotrace on
/
select * from X where NAME like 'x%';
--13 rows selected
--
----------------------------------------------------------------------------
--| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
--|   0 | SELECT STATEMENT  |      |     1 |    17 |     3   (0)| 00:00:01 |
--|*  1 |  TABLE ACCESS FULL| X    |     1 |    17 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

select /*+ INDEX( X  X_IX           ) */ * from X where   NAME like 'x%';
--13 rows selected
--
---------------------------------------------------------------------------
--| Id  | Operation        | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
--|   0 | SELECT STATEMENT |      |     1 |    17 |     9   (0)| 00:00:01 |
--|*  1 |  INDEX FULL SCAN | X_IX |     1 |    17 |     9   (0)| 00:00:01 |
---------------------------------------------------------------------------

select /*+ INDEX( X  X_IC           ) */ * from X where   NAME like 'x%'; 
--13 rows selected
--
--------------------------------------------------------------------------------------
--| Id  | Operation                   | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
--|   0 | SELECT STATEMENT            |      |     1 |    17 |   448   (1)| 00:00:06 |
--|*  1 |  TABLE ACCESS BY INDEX ROWID| X    |     1 |    17 |   448   (1)| 00:00:06 |
--|   2 |   INDEX FULL SCAN           | X_IC |  1629 |       |     8   (0)| 00:00:01 |
--------------------------------------------------------------------------------------
/

set autotrace off
/