Oracle-L: RE: skip scan index

From: Khedr, Waleed <Waleed.Khedr_at_FMR.COM>
Date: Wed, 28 May 2003 10:52:22 -0800
Message-ID: <F001.005A4A1E.20030528105222@fatcity.com>

Easy test case:

CREATE TABLE TEST_SKIP
(

    C1 NUMBER NOT NULL,
    C2 NUMBER NOT NULL,
    C3 NUMBER NULL
);

CREATE UNIQUE INDEX TESTSKIP1
ON TEST_SKIP(C1,C2); select --+ index_ss(test_skip, )
c1,c2,c3
from test_skip
where c2 = 10;

OPERATION                OPTIONS	 OBJECT_NAME
SELECT STATEMENT         [NULL]          [NULL]
TABLE ACCESS             BY INDEX ROWID  TEST_SKIP
INDEX                    SKIP SCAN       TESTSKIP1

Regards,

Waleed

-----Original Message-----
Sent: Wednesday, May 28, 2003 7:00 AM
To: Multiple recipients of list ORACLE-L

Okay, I have a developer here who has been reading the docs (this can be dangerous!)

we are adding functionality to one of our applications, this will involve using multiple fulfillment houses, so we'll be adding the fulfillment vendor id to the order table. Easy, this is not a problem. We want to be able to search by order date and by fulfillment vendor id/order date

Traditional design would be to add two indexes: one on order date, and a concatenated one on fulfillment vendor id/order date.

The developer is telling me to create a "skip scan index" instead of two different ones. MY reading in the FM tells me that skip scan index is not a type of index, but rather a way Oracle uses to use an index even if the leftmost column is not in the query.

Is there any benefit in my building only the one index? Our order volume is not so high (and never will be) that there is a visible performance impact if I have the two indices.

This is 9i, 9.2.0.1, will be upgrading to 9.2.0.2 in the near future. Solaris

Any suggestions/comments/war stories would be appreciated. I know I've seen Jonathan post on skip scan indexes before but I can't find the specific reference at the moment.

Rachel

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Author: Rachel Carmichael
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Author: Khedr, Waleed
INET: Waleed.Khedr_at_FMR.COM

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