From: | "Przemek " <krycek6(at)wp(dot)pl> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Syntax bug? Group by? |
Date: | 2006-10-18 10:59:11 |
Message-ID: | 453608fff0494@wp.pl |
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Lists: | pgsql-hackers |
Dnia 17-10-2006 o godz. 23:21 Tom Lane napisał(a):
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> > Mark Woodward wrote:
> >> My question, is it a syntactic technicality that PostgreSQL asks for a
> >> "group by," or a bug in the parser?
>
> > AFAIK what you want is not per sql spec.
>
> It would in fact be a violation of spec. Consider the case where there
> are no rows matching 15. In this case
>
> select min(tindex), avg(tindex) from y where ycis_id = 15;
>
> will yield one row containing NULLs, whereas
>
> select min(tindex), avg(tindex) from y where ycis_id = 15 group by
> ycis_id;
>
> will yield no rows (because there are no groups). Therefore, if
> Postgres were to implicitly insert a GROUP BY to make it legal to
> reference ycis_id directly, we'd be changing the query behavior
> and breaking spec.
>
> regards, tom lane
>
Hello
IMHO:
Also take into consider that - what should be expected behavior of this:
select ycis_id, min(tindex), avg(tindex) from y where ycis_id = truncate(random()*100);
Since result of comparission is not known on parsing phase it couldn't be done here if there is no other requirements on argum
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