Hello Mark

Thank for your answer.

But the strange thing is that PER_IDENTI is the Primary Key and ORDER BY
seems not use it.

Greetings.

Walter.

On Fri, Mar 1, 2013 at 4:18 AM, Mark Rotteveel <mark@...> wrote:

> **
>
>
> On Fri, 1 Mar 2013 00:37:26 -0400, W O sistemas2000profesional@...>
> wrote:
>
> > Somebody knows why there are a difference so big?
> >
> > I have a table with 3.600.000 rows more or less.
> >
> > Writing:
> > SELECT * FROM V_ABM_PERSONAS V WHERE V.PER_IDENTI > 0 ROWS 1 TO 100
> >
> > takes 2.656 seconds (less than 3 seconds)
> >
> > Writing:
> > SELECT * FROM V_ABM_PERSONAS V ORDER BY V.PER_IDENTI ROWS 1 TO 100
> >
> > takes more than 11 minutes!!!! (bored, I did cancel the execution)
> >
> > The column PER_IDENTI is the Primary Key.
> >
> > Why that? Why a difference so big? Somebody knows the answer?
> >
> > Windows 7, Firebird 2.5.1, SuperServer
>
> In the first example Fireibrd just needs to find the first 100 records
> that match V.PER_IDENTI > 0.
> In the second example, I guess it will retrieve all rows, sort them and
> then return the first 100 rows; ROWS probably is not optimized for an
> (index) ordered retrieval.
>
> Mark
>
>
>


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