Re: BUG #15143: Window Functions – Paranthese not allowed before OVER term

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От David G. Johnston
Тема Re: BUG #15143: Window Functions – Paranthese not allowed before OVER term
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Msg-id CAKFQuwZWOC5ev8vSwfof3B9RLQxJxj8VxjXtN97hb-x0tZ6aMg@mail.gmail.com
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Ответ на Re: BUG #15143: Window Functions – Paranthese not allowed before OVER term  (David Rowley <david.rowley@2ndquadrant.com>)
Ответы Re: BUG #15143: Window Functions – Paranthese not allowed before OVER term  (David Rowley <david.rowley@2ndquadrant.com>)
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On Wed, Apr 4, 2018 at 7:32 PM, David Rowley <david.rowley@2ndquadrant.com> wrote:
> Working as documented:
>
> "A window function call always contains an OVER clause directly following
> the window function's name and argument(s)"

Yeah, how else would the window function know which window clause it belongs to?

If you'd done: SELECT (LEAD(col) - LAG(col)) OVER (...)  could
PostgreSQL just assume that you meant to link both the lead and lag to
the same over clause?

​Well, if there is only a single aggregate function in the expression there isn't any ambiguity.  If there happened to be more than one the system could emit a parsing error saying as much.​  While likely more user-friendly I don't imagine its worth the headache in the parser.

I did kinda mis-speak earlier though - there probably aren't any expressions that require a window function to end up in a subquery, but usually if I get to the point of using complex expressions readability will lead me to do so.

David J.

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