前言：关于查询走不走索引里面有很多的东西，也分为很多种情况。这里只是简单的一个比较，后续会进一步分析。
1、创建表：SQL> create table test1 (id number,c1 varchar2(50),c2 varchar2(50),c3 varchar2(5
0),c4 varchar2(50));
2、模拟插入10000条记录：
SQL> begin
for i in 1..10000 loop
insert into test1 values(i,'阿斯顿飞就快了','及卡拉加水电费了健康','就爱看lsd减肥辣椒水代理费','阿斯顿飞卡死就到了费劲啊lsd就分开了');
end loop;
end;
/
3、打开执行计划，并查询：
SQL> set autotrace on;
SQL> select * from scott.test1 where id=500;
执行计划
----------------------------------------------------------
Plan hash value: 4122059633
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 242 | 42 (3)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| TEST1 | 2 | 242 | 42 (3)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("ID"=500)
Note
-----
- dynamic sampling used for this statement
统计信息
----------------------------------------------------------
171 recursive calls
0 db block gets
283 consistent gets
0 physical reads
0 redo size
708 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
4 sorts (memory)
0 sorts (disk)
1 rows processed
4、创建在id上的索引：
SQL> create index i_test1 on test1(id);
5、再次查询，并查看执行计划：
SQL> select * from scott.test1 where id=500;
执行计划
----------------------------------------------------------
Plan hash value: 550433309
--------------------------------------------------------------------------------
-------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Tim
e |
--------------------------------------------------------------------------------
-------
| 0 | SELECT STATEMENT | | 1 | 121 | 2 (0)| 00:
00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TEST1 | 1 | 121 | 2 (0)| 00:
00:01 |
|* 2 | INDEX RANGE SCAN | I_TEST1 | 1 | | 1 (0)| 00:
00:01 |
--------------------------------------------------------------------------------
-------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("ID"=500)
Note
-----
- dynamic sampling used for this statement
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
712 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
6、可以看到，创建索引后效率有很大提高。