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Date: Thu, 6 Apr 2017 21:52:30 -0400
From: Bruce Momjian <bruce@momjian.us>
To: "David G. Johnston" <david.g.johnston@gmail.com>
Cc: PostgreSQL-documentation <pgsql-docs@postgresql.org>
Subject: Re: Window function docs
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On Thu, Apr  6, 2017 at 06:43:38PM -0700, David G. Johnston wrote:
> On Thu, Apr 6, 2017 at 6:14 PM, Bruce Momjian <bruce@momjian.us> wrote:
> 
>     On Thu, Apr  6, 2017 at 03:53:24PM -0700, David G. Johnston wrote:
>    
>     > hypothetical-set aggregates as being distinct from ordered-set aggregates
>     yet
>     > the tables and the docs here do.
> 
>     Do you have any suggested text for that?
> 
> 
> - ​The built-in ordered-set aggregate functions are listed in Table 9-53 and
> Table 9-54.
> + The built-in ordered-set aggregate functions are listed in Table 9-53 while
> the built-in hypothetical-set ones are in Table 9-54.
> 
> That's a direct translation.  Reading some more, though, I think that:
> 
> + The built-in within-group aggregate functions are listed in Table 9-53
> (ordered-set) and Table 9-54 (hypothetical-set).

I went with this, for simplicity:

   The built-in within-group ordered-set aggregate functions
   are listed in <xref linkend="functions-orderedset-table">
   while the built-in within-group hypothetical-set ones are in <xref
   linkend="functions-hypothetical-table">.

> So now we'd have:
> 
> grouping-aggregates:
> normal aggregates (no suffix modifiers, though can embed ORDER BY in the
> aggregate function argument area)
> 
> within-group aggregates (requires WITHIN GROUP suffix modifier)
> ordered-set aggregates -> given parameters determine a record value, possibly
> imputed (within the defined group)
> hypothetical-set aggregates -> given a (virtual) record determine a parameter
> (within the defined group)
> 
> non-grouping aggregates:
> window aggregates (requires OVER suffix modifier)
> 
> The CREATE AGGREGATE only names those three specific types in the notes
> section.

Yes, very complicated.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +


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