2010/9/22 Dennis Björklund <db@zigo.dhs.org>:
> In
>
> http://www.postgresql.org/docs/9.0/static/tutorial-window.html
>
> it say
>
> "Although avg will produce the same result no matter what order it
> processes the partition's rows in, this is not true of all window
> functions. When needed, you can control that order using ORDER BY within
> OVER."
>
> While it's true that avg() produce the same result no matter what order. A
> ORDER BY clause will affect what rows are included in the computation and
> thus change the result (the default window frame is
> RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW). So one can not in
> general add an ORDER BY to the example in the tutorial and get the same
> result as without an ORDER BY.
>
> Maybe we can find some better wording of the above?
Your point is true, but I believe it's still ok because the section is
a tutorial for novices. If you start to explain everything here,
readers don't want to read it to the end.
Regards,
--
Hitoshi Harada