Re: SQL confusion

On Sat, Oct 09, 2004 at 01:39:45PM -0700, Andrew Ward wrote:
>
> 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)
>
> CREATE TABLE name (
> namecounter integer NOT NULL,
> firstmiddle character varying(64) NOT NULL,
> lastname character varying(64) NOT NULL,
> birthdate date,
> hh smallint,
> famnu integer,
> );

This may not be the fastest query, but it should be quite comprehensible.
Lightly tested only on 7.4.5 (do you know why you're not using 7.4.x?).

SELECT namecounter -- and whatever other columns you need
FROM name outername -- alias so it's clear what the joins do
WHERE hh = 1 -- simple case: head of family
OR (
hh = 0 -- not a head
AND NOT EXISTS ( -- there is no head of this family
SELECT namecounter
FROM name in1
WHERE hh = 1 AND in1.famnu = outername.famnu)
AND birthdate = ( -- this person is as old as the oldest person
SELECT MIN(birthdate)
FROM name in2
WHERE in2.famnu = outername.famnu)
);

Richard