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Re: Teach SELECT DISTINCT first!

From: Laconic2 <laconic2_at_comcast.net>
Date: Thu, 29 Apr 2004 09:02:17 -0400
Message-ID: <-6Cdnf1n6489YQ3dRVn-gg@comcast.com>


OK, consider the following:

How do you represent a set inside of a computer?

One way is to use a bitmap. Take the power set of the inital set, assign each element of the
power set a binary number, and do it in such a way that the individual bits correspond to the individual
elements of the original set.

Now you can represent any subset of the original set as a binary number. Yes, but you've sorted
the original set, as well. If you ask the question

{pepperoni, onion} ?= {onion, pepperoni}

and you use a bitmap representation to answer the question, you are going to end up sorting.

Is this clear? Received on Thu Apr 29 2004 - 08:02:17 CDT

Original text of this message

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