From: | daq <daq(at)ugyvitelszolgaltato(dot)hu> |
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To: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: retrieving primary key for row with MIN function |
Date: | 2009-04-29 15:41:52 |
Message-ID: | 146186391968.20090429174152@ugyvitelszolgaltato.hu |
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Lists: | pgsql-novice |
MK> Hello everyone,
MK> I need to retrieve PK (r.id in the query) for row with
MK> MIN(r.start_date), but with a twist: I need to select only one record,
MK> the one with minimum date.
MK> Doing it like this does not solve the problem:
MK> SELECT h.id AS host_id, MIN(r.start_date) AS reservation_start_date,
MK> r.id AS reservation_id
MK> FROM hosts h
MK> LEFT OUTER JOIN reservation_hosts rh ON rh.host_id = h.id
MK> LEFT OUTER JOIN reservation r ON r.id = rh.reservation_id AND
MK> (r.start_date, r.end_date) OVERLAPS ('2009-04-29'::date, '2010-04-29'::date)
MK> GROUP BY h.id, r.id
MK> ORDER BY reservation_start_date ASC
MK> I have to use either GROUP BY r.id or use MIN(r.id). MIN(r.id) doesn't
MK> select the id from the row with corresponding MIN(r.start_date), so it's
MK> useless, while GROUP BY r.id produces more than one row:
MK> host_id reservation_start_date reservation_id
MK> 361 2009-05-11 38
MK> 361 2009-05-17 21
MK> I need to select only row with reservation_id = 38.
MK> I would rather not do subquery for every 'host' record, since there can
MK> be a lot of them...
MK> Regards,
MK> mk
I think, the key is:
SELECT id FROM reservation WHERE start_date=(íselect min(start_date)
FROM reservation);
You got the id. Use it well! :)
DAQ
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