Kalen Delaney : Did You Know? Statistics vs Indexes

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Kalen Delaney

Did You Know? Statistics vs Indexes

What is the difference between statistics and indexes? Do auto created statistics indicate that you should build an index?

I will be posting answers to some of the interesting questions I get from my students and my readers (these are not two disjoint sets, of course) on the new SQLCommunity site.

Check out this the answer to this question at:

http://www.sqlcommunity.com/Articles/SQLServerArticlesCategorized/tabid/153/language/en-US/Default.aspx

The article has some geeky stuff in it too. For example, it explains how to interpret the strangely named statistics, such as _WA_Sys_00000010_2EDAF651.

Have fun!

~Kalen

Published Monday, February 04, 2008 12:44 PM by Kalen Delaney

Filed under: statistics, indexes

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	James Luetkehoelter said: Ah, the _WA indexes :) I once had a client insisting that they should be deleted and were wasting space...and he was the senior DBA for that company! Didn't know about the sqlcommunity website, is that new? Would they accept longer, non-blog like articles from the likes of a lowly me? February 5, 2008 9:46 AM
	Kalen Delaney said: Hi James Yes, I continue to see lots of confusions about the automatically built stats, and column stats in general. I have a script I run in class that shows a query running much worse when auto create stats is turned off., I blogged about SQLCommunity just a few weeks ago: http://sqlblog.com/blogs/kalen_delaney/archive/2008/01/19/did-you-know-a-terrific-new-community-website.aspx We'd love to have your contributions! Thanks Kalen February 5, 2008 11:18 AM
	Jason Haley said: February 5, 2008 1:15 PM
	em81 said: Kalen, When the statistics are generated on a index doesn't it choose a sample of 200 rows initailly or is it a different number? What ever sample number it uses how does it come about choosing those rows? February 5, 2008 2:07 PM
	Kalen Delaney said: Hi em81 When statistics are being generated, SQL Server will select up to 200 values. How it chooses them is part of the internal algorthm which MS does not make public. You can read this Whitepaper for more details: Statistics Used by the Query Optimizer in Microsoft SQL Server 2005 http://www.microsoft.com/technet/prodtechnol/sql/2005/qrystats.mspx February 6, 2008 6:34 PM

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Kalen Delaney

Did You Know? Statistics vs Indexes

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