From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
Cc: | Mark Woodward <pgsql(at)mohawksoft(dot)com>, Shane Ambler <pgsql(at)007Marketing(dot)com>, pgsql-hackers(at)postgresql(dot)org, sfrost(at)snowman(dot)net |
Subject: | Re: Syntax bug? Group by? |
Date: | 2006-10-17 21:21:53 |
Message-ID: | 11881.1161120113@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
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
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