Re: Question about Append hint in Insert

From: Daniel Fink <Daniel.Fink_at_Sun.COM>
Date: Mon, 21 Jun 2004 12:55:28 -0600
Message-id: <40D72F20.4040905@sun.com>

One other 'subtle' difference in this scenario is that you cannot perform an INDEX UNIQUE SCAN on the index when you are using an equality predicate. IIRC, the CBO will cost the allowable RANGE SCAN the same as the UNIQUE SCAN so there should not be differences in query plan selection nor execution time. If you are using explain plan/tkprof, etc. you will see a drastic difference in the card(inality) estimate, but this does not really factor in to the equation (in this case).

Also, to keep things clear and supportable, make sure to document the reason for doing this.

Regards,
Daniel

jaromir nemec wrote:
> Hi Lex,
>
> Thanks for the correction of my misinterpretation.
> Does it mean there are no other differences or things to keep in mind when
> deciding between unique and non-unique index to support unique constraint?
>
> Thanks
> Jaromir D.B.Nemec
>
>
>

>>one small correction: non-unique indexes do *not* allocate more space...

>
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>
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Received on Mon Jun 21 2004 - 13:52:49 CDT