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From: Tom Lane <tgl@sss.pgh.pa.us>
To: John Lumby <johnlumby@hotmail.com>
Cc: pgsql-docs@lists.postgresql.org <pgsql-docs@lists.postgresql.org>
Cc: David G. Johnston <david.g.johnston@gmail.com>
Subject: Re: description of Aggregate Expressions
Date: Fri, 06 Dec 2019 14:17:35 -0500
Message-ID: <382.1575659855@sss.pgh.pa.us> (raw)
In-Reply-To: <DM6PR06MB55621D8E8B9C786DAA6BA077A35F0@DM6PR06MB5562.namprd06.prod.outlook.com>
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John Lumby <johnlumby@hotmail.com> writes:
> On 12/05/19 18:06, David G. Johnston wrote:
>> Then I would have to say the proposed solution to this edge case is worse than the problem.  I also don't expect there to be a clean solution to dealing with the complexities of expressions at the syntax diagram level.

> Yes,  I see what I suggested is not ideal either.     But I think something needs to be changed.

> How about replacing "expression [ , ... ]"  by "parameter_list" in the description, and then stating that parameter_list can be either a single expression or ,   if the particular aggregate function accepts it (for which,   consult that function's reference),    a comma-separated list of expressions.

That's just as wrong.  As we tried to explain before, the
parenthesized-list syntax is a row constructor, so it only works
in cases where the aggregate function can accept a composite
argument type.  Most don't.

Moreover, the very same thing holds in *any* expression context,
not only aggregate arguments.  So if we took this seriously there
would have to be a lot of other places plastered with equally
confusing/unhelpful addenda.

			regards, tom lane





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