Re: Explain Plan question

On Sun, 21 Apr 2002 17:38:44 +0100, Jayne Heger <jayne.heger_at_spamAndChips.ntlworld.com> wrote:

>
>Hi,
>
>I have ran an Explain query on three quesries to test which one would be
>the most efficient to use.
>
>The 1st query, had a cost of 26
>second one = 10006
>third one = 7347
>
>Now, to my understanding, the 1st one would be the most efficient.
>But I have also ran a timer on each of the queries, and the 1st query took
>the longest time by far.
>1st query = 00:11:58:39
>2nd query = 00:00:08:42
>3rd query = 00:00:08:80
>
>would it be because of the network load that the 1st query took so long?
>
>Can anyone explain this, i am a bit puzzled?
>
>Thanks
>
>Jayne
>

Hi Jayne,

cost is specific to only one query. You can't compare the costs of different queries.

The Cost Based Optimizer evaluates n execution plans for a specific query. It calculates the cost for each execution plan. The one with the lowest cost wins and is to be used.

regards
Marc Blum
mailto:marc_at_marcblum.de
http://www.marcblum.de Received on Sun Apr 21 2002 - 14:20:16 CDT