From: Josh Berkus <josh@agliodbs.com>
To: Peter Eisentraut <peter_e@gmx.net>
To: Dan Langille <dan@langille.org>
Cc: Chad Thompson <chad@weblinkservices.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: 7.3 "group by" issue
Date: Sat, 22 Feb 2003 11:34:45 -0800
Message-ID: <200302221134.45226.josh@agliodbs.com> (raw)
In-Reply-To: <Pine.LNX.4.44.0302220245460.2067-100000@peter.localdomain>
References: <Pine.LNX.4.44.0302220245460.2067-100000@peter.localdomain>
Peter,
> This does not work because the first select list item references a column
> inside a join, which is not (necessarily) mathematically identical to the
> column that arrives outside of the join and is in the GROUP BY clause.
> (Think of an outer join: the column outside the join might contain added
> null values. Of course you are using an inner join, but the constructs
> work the same either way.)
Hmmm ... I don't see that. I can see that it might be practically
difficult-to-impossible to make the planner distinguish between cases where
the columns in the select list are different from the columns in the JOIN
series and when they aren't, but as a theory issue I just don't buy it.
What Dan's doing is:
SELECT a.c1, count(a.c2)
FROM a JOIN b
WHERE b.c5 = x
GROUP BY c1
In a case like this, a.c1 == c1 without possibility of ambiguity. The only
difference is whether or not a table qualifier is used on the name, which in
theory should *only* make a difference when there are more than one table in
the query with that column name.
So if you're saying that that kind of equivalency is a challenging parser
implementation issue, then I'm with you. If you're saying its a SQL theory
issue, though, I don't agree at all.
--
Josh Berkus
Aglio Database Solutions
San Francisco
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To: pgsql-sql@postgresql.org
Cc: josh@agliodbs.com, peter_e@gmx.net, dan@langille.org, chad@weblinkservices.com
Subject: Re: 7.3 "group by" issue
In-Reply-To: <200302221134.45226.josh@agliodbs.com>
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