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