Re: Creating unique index on huge table.

Hi Jonathan,
Histograms are created for columns, not for indexes. So if there is a unique compound index, comprised of several columns, the histograms may still be useful. I completely agree with you. Did I understand you correctly that Oracle will create histograms for the underlying columns, if needed? Thanks, this is good to know. I have never checked. Regards

On 09/24/2016 02:16 AM, Jonathan Lewis wrote:
>
>
> Just for the record - uniqueness doesn't automatically mean that a
> histogram will be unnecessary; moreover if a histogram on a unique
> column is necessary Oracle will detect it build it during a default
> "gather_table_stats".
>
>
> Regards
> Jonathan Lewis
> http://jonathanlewis.wordpress.com
> _at_jloracle
> ------------------------------------------------------------------------
> *From:* oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org]
> on behalf of Mladen Gogala [gogala.mladen_at_gmail.com]
> *Sent:* 24 September 2016 02:55
> *To:* oracle-l_at_freelists.org
> *Subject:* Re: Creating unique index on huge table.
>
> And the data distribution for the unique index is trivial and does not
> need statistics. Hopefully, you didn't create histograms on the unique
> index?
>
>

-- 
Mladen Gogala
Oracle DBA
Tel: (347) 321-1217


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