FAQ
Thanks a lot Naveen,

Even after executing the following the execution plan shows full table scan :-

+ alter session set QUERY_REWRITE_ENABLED=TRUE;
+ alter session set QUERY_REWRITE_INTEGRITY=TRUSTED;
+ alter session set optimizer_mode=FIRST_ROWS;
+ Insert into employees values('A');
+ Insert into employees values('B');
+ analyze table employees compute statistics;
+

select last_name
FROM employees WHERE UPPER(last_name) IS NOT NULL
ORDER BY UPPER(last_name); 2 3
Elapsed: 00:00:00.00

Execution Plan

0 SELECT STATEMENT Optimizer=FIRST_ROWS (Cost=3 Card=2 Bytes=2
)

1 0 SORT (ORDER BY) (Cost=3 Card=2 Bytes=2)
2 1 TABLE ACCESS (FULL) OF 'EMPLOYEES' (Cost=1 Card=2 Bytes=
2)

Even after using the hint no change in the plan :-
+ select /* INDEX employees(upper_ix) */ last_name FROM employees WHERE UPPER(last_name) IS NOT NULL;

Please tell me what else should I do to make this query use the index which is created.

TIA,

Marul.

Original Message -----
From: Naveen Nahata
To: Multiple recipients of list ORACLE-L
Sent: Saturday, August 31, 2002 3:03 PM
Subject: RE: Function-Based Index not working

Marul,

you don't have table analyzed in which case Rule based optimizer will be used. CBO is used if atleast one of the tables in the query is ANALYZED
There is no data in your table. Optimizer goes for a full tablescan if it thinks that it will be moer advisable to do a full table scan. e.g. You will not use the INDEX if your book has only one page.

The decision of going for a full tablescan is based on DB_BLOCK_SIZE * DB_FILE_MULTI_BLOCK_READCOUNT, which tells how much data Oracle fetches at one time. If your entire table can be fetched in atleast 2 fetches, full table scan will be done instead of INDEX scan, to avoid doubling of work.

Naveen
-----Original Message-----
From: Marul Mehta
Sent: Saturday, August 31, 2002 2:18 PM
To: Multiple recipients of list ORACLE-L
Subject: Function-Based Index not working

Hi,

Can you please help me out in solving this weird problem of funcation-based index not being used when I query the table.
This is the comand I fired and the result it returned me.

SQL> create table employees (last_name varchar2(20));
Table created.

SQL> CREATE INDEX upper_ix ON employees (UPPER(last_name));
Index created.

Made the autotrace on and than:-

3. SELECT last_name FROM employees WHERE UPPER(last_name) IS NOT NULL ORDER BY UPPER(last_name);

no rows selected.

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (ORDER BY)
2 1 TABLE ACCESS (FULL) OF 'EMPLOYEES'

I fired without order by clause also but no use.

Now can any body please let tell me why this Oracle is having a full scan of the employee table.

TIA,

Marul.



--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Marul Mehta
INET: marul_at_zycus.com

Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).

Search Discussions

Discussion Posts

Previous

Follow ups

Related Discussions

Discussion Navigation
viewthread | post
posts ‹ prev | 4 of 12 | next ›
Discussion Overview
grouporacle-l @
categoriesoracle
postedAug 31, '02 at 8:48a
activeAug 31, '02 at 3:13p
posts12
users5
websiteoracle.com

People

Translate

site design / logo © 2022 Grokbase