From: | Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com> |
---|---|
To: | Dennis Björklund <db(at)zigo(dot)dhs(dot)org> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Documentation, window functions |
Date: | 2010-09-22 16:54:45 |
Message-ID: | AANLkTik3xiDTDrkj=0iM0NPj-6TUCMPFznRykQwbp7q0@mail.gmail.com |
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2010/9/22 Dennis Björklund <db(at)zigo(dot)dhs(dot)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
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