Re: Views - performance

From: Robert Klemme <shortcutter_at_googlemail.com>
Date: Thu, 07 Sep 2006 13:24:47 +0200
Message-ID: <4madrvF2l21dU1@individual.net>

On 07.09.2006 11:15, Martin T. wrote:

> Robert Klemme wrote:

>> A disadvantage of views which I sometimes encounter is the fact that a
>> join in the view will always be performed - even if you do not query
>> columns from that table. This can sometimes decrease performance if the
>> join does not change the set of data from the other table (e.g. if there
>> is a n:1 relationship between a fact table and a dimension table in DWH
>> applications).
>>

> 
> I was under the impression that the xplan Oracle comes up with will be
> _exactly_ the same regardless of having a view or an inline view (of
> course only if both i-v. an v. are exactly the same) ... ?

Yes, that should be the case (at least in theory; there might be other factors that change the picture like stored outlines etc.). My point was more like you can change (optimize) the query (and thus the plan) if you explicitly join only tables that you are actually pulling data from if you know that the result doesn't change.

Kind regards

robert Received on Thu Sep 07 2006 - 06:24:47 CDT