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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?


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