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AW: AW: [HACKERS] correlated subquery

From: Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at>
To: "'hackers(at)postgresql(dot)org'" <hackers(at)postgreSQL(dot)org>
Subject: AW: AW: [HACKERS] correlated subquery
Date: 1999-12-31 08:39:40
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
> Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at> writes:
> >> It finds the oldest person in each state.  HAVING can't do 
> >> that, right?
> > Having can do that particular case: (e.g. Informix)
> >        SELECT f1.firstname, f1.lastname, f1.age
> >        FROM friends f1, friends f2
> >        WHERE f1.state = f2.state
> >        GROUP BY f2.state, f1.firstname, f1.lastname, 
> f1.age, f1.state
> >        HAVING f1.age = max(f2.age)
> >        ORDER BY firstname, lastname;
> Hmm, yes, and you don't even need the GROUP BY state clauses.
> But it's not really the same thing.  In particular, if you 
> had two friends
> with the same name and age, this would produce only one output record
> for both, not two output records as Bruce's original query does.
> That's neither likely nor a big problem in the hypothetical 
> application,
> but other applications needing this type of query might be 
> more unhappy
> about confusing similar records...

Yes, it only gives the same result, if "f1" has some sort of primary key
(e.g. oid),
that can be put into the group by clause.


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