RE: frequency + height based histograms.
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <sjaffarhussain@xxxxxxxxx>
- Date: Mon, 6 Mar 2006 12:55:24 +0100
Jaffar
>I was reading Jonathan's great book, at least for me, 'CBO
>Fundamentals' and I got confused of frequency/height based histograms,
>though he explained in a great way.
What is confusing is the name given by Oracle ;-)
>What I understood is that, if we have more than 254 distinct values in
>a columns, we use height based histograms and when we have less than
>254 distinct values in a column, we use one bucket for 1 distinct
>value. Are my assumption are correct, or am I missing something?
if
"1 distinct value per bucket"
then
"frequency"
else
"height-based"
end if
i.e. you may have a height-based histogram even if there are "only" 50 or 100
distinct values. It depends on how you created it.
HTH
Chris
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