Re: Histogram Q
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: sacrophyte@xxxxxxxxx
- Date: Wed, 13 Dec 2006 10:50:28 -0700
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@xxxxxxxxxxx>Brandon.Allen@xxxxxxxxxxx> 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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