## Message Posted: Mon, 19 Jan 2004 @ 15:20:52 GMT

 < Last>>

 Subj: Re: V2R5 Statistics From: Victor Sokovin

Craig,

Mathematically these are two quite different things. Let me explain the difference using the simplest example.

Table T had two columns, A and B, each of which can only take values 0 and 1. T has 100 rows, and 0 and 1 are distributed evenly in A and B, i.e., there exactly 50 0 and 50 1 in both A and B.

Now, take all possible values of the pair (A,B):

(0,0)
(0,1)
(1,0)
(1,1)

I can have quite different tables of this kind:

T1 has only (0,0) and (1,1), they occur 50 times each;

T2 has all 4 combinations (0,0), (0,1), (1,0), (1,1), 25 times each.

Obviously, T1 and T2 are quite different tables but their one-dimensional projections are the same (50 0s and 50 1s in 100 rows). When you collect multi-column statistics you should get more accurate (multidimensional) information (at least let's hope so!). Single-column statistics describe projections only and they might be missing something important.

Regards,

Victor

 < Last>>

Attachments

Library

Quick Reference

Archives

Sample Index

 2016 2007 2015 2006 2014 2005 2013 2004 2012 2003 2011 2002 2010 2001 2009 2000 2008 1999

2004 Indexes

 Jan Jul Feb Aug Mar Sep Apr Oct May Nov Jun Dec

 Top Home Privacy Feedback