Re: TODO items for window functions

2008/12/29 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> I wrote:
>> * Support creation of user-defined window functions. I think this is
>> a "must have" for 8.4 --- we are not in the habit of building
>> nonextensible basic features. It doesn't seem that hard either.
>> I think all we need do is to allow "WINDOW" as an attribute keyword
>> in CREATE FUNCTION. Does anyone have an objection or a better idea?
>
> What I had in mind when I wrote that was something like
>
> create [or replace] function mywindow(...) returns ...
> as 'mymodule, 'mywindow'
> language c
> window;
>

+1

regards
Pavel Stehule

> but on reflection there seems to be a case also for
>
> create [or replace] window function mywindow(...) returns ...
> as 'mymodule, 'mywindow'
> language c;
>
> The main argument in favor of the latter is that window-ness will need
> to be a fixed property of a function that you can't change except by
> dropping and recreating it, because any existing views calling the
> function will have its window-ness embedded in them in the form of
> whether they use a FuncExpr or WindowFunc node to call it. So it
> doesn't feel quite like an optional attribute.
>
> However, if we do that then for consistency we'd have to invent
> DROP WINDOW FUNCTION, ALTER WINDOW FUNCTION, RENAME WINDOW FUNCTION,
> COMMENT ON WINDOW FUNCTION, yadda yadda, and insist that you refer
> to a function properly (with or without WINDOW) in each one of these
> commands. Which would be a real PITA to implement and document,
> and I can't see that it's doing anything much for users either.
>
> So I'm still leaning to the first way. Comments?
>
> regards, tom lane
>
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