I believe you were asking about ordering, not selecting. The answer is it depends. If your order by clause matches an index key then sql will take advantage of that index. You sql could run slower if you order by a key that doesn't match any indices. Logically, lot, case, piece makes more sense.
-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of George Kinney
Sent: Thursday, September 01, 2011 4:50 PM
To: midrange-l@xxxxxxxxxxxx
Subject: Order of key fields
Here's the situation, I have a table that has a 12 field index. Some of
those fields are far more variable than others, and at the moment they
are specified in the DDS in the order they appear in the source data.
What I'm wondering is if there is a signifigant performance advantage
(or penalty) to ordering them according to their variability. In other
words, given a situation where you have a lot#, case#, piece# with many
pieces# per case, per lot, would a key order of (lot, case, piece)
affect performance differently than (piece, case, lot)?
Anybody know, or have any pointers to enlightening online resources?
--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit:
http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at
http://archive.midrange.com/midrange-l.
________________________________
Notice from Bob Evans Farms, Inc: This e-mail message, including any attachments, may contain confidential information that is intended only for the person or entity to which it is addressed. Any unauthorized review, use, disclosure or distribution is strictly prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message and any attachments.
midrange.com
