Re: Histogram Q

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Wed, 13 Dec 2006 10:50:28 -0700
Message-Id: <20061213174943.DBDB156A6D4@turing.freelists.org>

Charles,

I suspect you are referring to the case when you (or size skewonly) collect a histogram requesting more than 1 bucket for a column with num_distinct=1 (all rows have the same value for that column). You'll get a histogram with one single row in dba_histograms - a 'size 1' "histogram" has two rows in dba_histogram - which is really a frequency histogram (as it should be when size > num_distinct) but is labelled a HB histogram in dba_tab_columns.histogram.

At 10:29 AM 12/13/2006, Charles Schultz wrote:
>Be careful with that. It is possible to have a height-balanced
>histogram with one bucket, according some of those views. Granted,
>it is not really a histogram at all, but the views have some funky
>logic in them.
>
>On 12/13/06, Allen, Brandon
><<mailto:Brandon.Allen_at_oneneck.com>Brandon.Allen_at_oneneck.com> wrote:
>You are correct - 1 bucket = "no histogram". You can also query for
>user_tab_columns.histogram = 'NONE' to confirm.

Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com

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Received on Wed Dec 13 2006 - 11:50:28 CST