On Fri, Aug 12, 2005 at 18:57:34 +0100,
  Nick Stone <[EMAIL PROTECTED]> wrote:
> Hope this helps
> 
> SELECT
>       *
> FROM
>       speed_history as outside etc..
> WHERE
>       (speed = (
>               SELECT
>                       speed
>               FROM
>                       speed_history as inside etc..
>               WHERE
>                       (outside.interface = inside.interface)
>               LIMIT 1
>               ORDER BY
>                       speed DESC
>               )
>       )
> 
> Hopefully you get the idea - basically it's a corelated sub-query - very
> useful
> 

Note that you want to order by interface DESC, speed DESC in the subselect
and have an index on (interface, speed) for this to really be efficient.
I think 8.1 might be smart enough to use an index on (interface, speed)
in the above case, but currently released versions won't.

---------------------------(end of broadcast)---------------------------
TIP 3: Have you checked our extensive FAQ?

               http://www.postgresql.org/docs/faq

Reply via email to