Thks, is a great appendix for all the prior messages,

And is definetively the explanation and solution.

Tks very much

--- In firebird-support@yahoogroups.com, Christian Mereles <chmereles@...> wrote:
>
> Ok, some querys:
>
> 1 - No index:
>
> select coalesce(max(o.N_ORDEN), 0) + 1 from ORDENES O
> where O.EJER=2012 --into new.n_orden
>
> https://dl.dropboxusercontent.com/u/15932768/sin_indice.jpg
>
> 2 - With index, uses multiple records:
>
> create descending index ordenes_idx1 on ordenes (ejer,n_orden);
> select coalesce(max(o.N_ORDEN), 0) + 1 from ORDENES O
> where O.EJER=2012
>
> https://dl.dropboxusercontent.com/u/15932768/usa_indice_muchos.jpg
>
> 3 - With index, use only 1 record:
>
> create descending index ordenes_idx1 on ordenes (ejer,n_orden);
> select first 1 coalesce(o.n_orden,0) + 1 from ordenes o
> where o.ejer=2012
> order by o.ejer desc, o.n_orden desc
> --into new.n_orden;
>
> https://dl.dropboxusercontent.com/u/15932768/usa_indice_uno.jpg
>
> Regards.
>
> Christian.
>
>
> [Non-text portions of this message have been removed]
>