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

On Wed, Apr 4, 2018 at 7:32 PM, David Rowley <david(dot)rowley(at)2ndquadrant(dot)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.