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Re: TODO items for window functions

From: "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Andrew Dunstan" <andrew(at)dunslane(dot)net>, "David Fetter" <david(at)fetter(dot)org>, "Hitoshi Harada" <umi(dot)tanuki(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: TODO items for window functions
Date: 2008-12-31 08:20:41
Message-ID: 162867790812310020y1f52dd9dnb0106d82d7630979@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
2008/12/31 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> "Robert Haas" <robertmhaas(at)gmail(dot)com> writes:
>>> Apparently that analogy didn't impress anyone but me.
>
>> It impressed me.  I liked making WINDOW a flag that occurs later in
>> the statement a lot better.
>
> I ended up going with the flag/attribute approach.  The other would be
> only marginally more work now, but I remain convinced that we'd have to
> do more work later to deal with the issue that CREATE WINDOW FUNCTION
> looks like "window function" is a distinct kind of SQL object.  And
> nobody seemed to want to propagate that distinction into all the places
> it would logically have to go.
>
> However ... having said that, there is more to David Fetter's gripe
> about \df than I realized at first.  Consider
>
> regression=# \df nth_value
>                        List of functions
>   Schema   |   Name    | Result data type | Argument data types
> ------------+-----------+------------------+---------------------
>  pg_catalog | nth_value | anyelement       | anyelement, integer
> (1 row)
>
> Even without any consideration of user-defined window functions,
> this seems a bit lacking: the user of nth_value() needs to know that
> he has to write an OVER clause, and as things stand \df is not going
> to give him the slightest hint about that.  So I can see the argument
> for reflecting window-ness into \df somehow.
>
> I am not thrilled about inventing a new column for this, but how about
> a display like so:
>
> regression=# \df nth_value
>                        List of functions
>   Schema   |   Name    | Result data type |       Argument data types
> ------------+-----------+------------------+---------------------------------
>  pg_catalog | nth_value | anyelement       | anyelement, integer OVER window
>

+1

regards
Pavel Stehule

> or some other addition that only shows up when needed.
>
>                        regards, tom lane
>
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