Re: Creating unique index on huge table.

  • From: Mladen Gogala <gogala.mladen@xxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Sat, 24 Sep 2016 02:49:04 -0400

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
@jloracle
------------------------------------------------------------------------
*From:* oracle-l-bounce@xxxxxxxxxxxxx [oracle-l-bounce@xxxxxxxxxxxxx] on behalf of Mladen Gogala [gogala.mladen@xxxxxxxxx]
*Sent:* 24 September 2016 02:55
*To:* oracle-l@xxxxxxxxxxxxx
*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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