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Re: SQL confusion

From: Thomas F(dot)O'Connell <tfo(at)sitening(dot)com>
To: Andrew Ward <adward555(at)yahoo(dot)com>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: SQL confusion
Date: 2004-10-12 17:01:06
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-sql
This is untested, but it might be enough to get you started:

SELECT namecounter
FROM name n
	FROM name
	WHERE hh > 0
	AND famnu = n.famnu
GROUP BY famnu
HAVING birthdate = min( birthdate );

What I'm trying to do here is grab all families that don't have a head 
of household, group them by family, and get only the namecounter 
corresponding to the minimum birthdate for that family.

If I recall, I've had some trouble using HAVING with min/max in ways 
that seem intuitive to me, but this might help get you started.


On Oct 9, 2004, at 3:39 PM, Andrew Ward wrote:

> I'm trying to figure out how to do a particular query,
> and I'm beating my head against a wall.  Here's my
> situation:
> I'm running postgres 7.3.2 on linux, and making my
> requests from Perl scripts using DBD::Pg.  My table
> structure is as follows (irrelevant cols removed)
>     namecounter integer NOT NULL,
>     firstmiddle character varying(64) NOT NULL,
>     lastname character varying(64) NOT NULL,
>     birthdate date,
>     hh smallint,
>     famnu integer,
> );
> Each row represents a person with a unique
> namecounter.  Families share a famnu, and usually one
> person in a family is marked as head of household
> (hh>0), with everyone else hh=0.  However, there are a
> few families with nobody marked as hh, and I'd like to
> elect one by age.  The query I'm trying to do is to
> pull one person from each household, either the head
> of household if available, or the eldest if not.  I
> want them sorted by last name, so I'd prefer to find
> them all in one query, no matter how ugly and nested
> it has to be.
> I can pull the list with hh>0 easily enough, but I'm
> not sure how to pull out the others.
> I realize that this could be done through some looping
> in the Perl script, but I'd like to avoid pulling the
> whole list into memory in case the list gets long.  My
> preference is to just handle one record at a time in
> Perl if possible.
> Help?
> Andrew Ward
> adward55(at)yahoo(dot)com
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In response to

pgsql-sql by date

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Subject: Re: Information about the command SQL " create synonym".
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Subject: JDBC +CIDR

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