From: John Lumby <johnlumby@hotmail.com>
To: "pgsql-docs@lists.postgresql.org" <pgsql-docs@lists.postgresql.org>
CC: "David G. Johnston" <david.g.johnston@gmail.com>, Tom Lane
	<tgl@sss.pgh.pa.us>
Subject: Re: description of Aggregate Expressions
Thread-Topic: description of Aggregate Expressions
Thread-Index: AQHVq8Cfp39padbrW02rHVPPdQZZdaetcyGAgAAI/4CAAAlrq4AAHqS6
Date: Fri, 6 Dec 2019 21:43:59 +0000
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John Lumby wrote:=0A=
<  =0A=
< Tom Lane wrote=0A=
< =0A=
< > > How about replacing "expression [ , ... ]"  by "parameter_list" in th=
e description, =0A=
< > > and then stating that parameter_list can be either a single expressio=
n or , =0A=
< > >  if the particular aggregate function accepts it (for which,   consul=
t that function's reference),=0A=
< > >   a comma-separated list of expressions.=0A=
< > =0A=
< > That's just as wrong.  As we tried to explain before, the=0A=
< > parenthesized-list syntax is a row constructor, so it only works=0A=
< > in cases where the aggregate function can accept a composite=0A=
< > argument type.  Most don't.=0A=
< >=0A=
< =0A=
< But surely not *all* cases of a multi-expression parameter list of an agg=
regate function are row constructors are they?    What about=0A=
< =0A=
< select parent_id, name, GROUPING(parent_id , name), count(*) FROM mytable=
 GROUP BY ROLLUP(parent_id , name);=0A=
< =0A=
< In the piece "GROUPING(parent_id , name)" ,=0A=
<   is "(parent_id , name)"  a row constructor or a list of two expressions=
?=0A=
< =0A=
< Or are you saying those are one and the same thing?=0A=
< =0A=
=0A=
I think I can answer my own question   -  No they are not the same  -   bec=
ause :=0A=
=0A=
select parent_id, name, GROUPING(ROW(parent_id , name)), count(*) FROM myta=
ble GROUP BY ROLLUP(parent_id , name);=0A=
ERROR:  arguments to GROUPING must be grouping expressions of the associate=
d query level=0A=
LINE 1: select parent_id, name, GROUPING(ROW(parent_id , name)), cou...=0A=
                                         ^=0A=
=0A=
=0A=