why does oracle not use the index pk_emp

From: <zhangguoping_at_boco.com.cn>
Date: Thu, 27 Mar 2003 11:37:19 +0800
Message-ID: <b5trgb$1rs7$1@mail.cn99.com>

i exec following sql in scott/tiger:

"explain plan for select empno from emp"

but it shows

---

| Id | Operation | Name | Rows | Bytes | Cost |

---

|   0 | SELECT STATEMENT     |             |    82 |  1066 |     2 |
|   1 |  TABLE ACCESS FULL   | EMP         |    82 |  1066 |     2 |


--------------------------------------------------------------------

Note: cpu costing is off

why doesn't it perform full index scan since pk_emp contain the empno needed!
by the way, what 's meaning of "Note: cpu costing is off"?????

i am a freshman, thks! Received on Wed Mar 26 2003 - 21:37:19 CST