Re: simple (?) join

Hello, Gary.

thank you for your e-mail

This is a slightly modified version of the query I sent you on first place
(have you tried it out?).

It will return (I hope :) the full orders record plus the maximum
ol_timestamp and respective o_user.

HTH
Best,
Oliveiros

SELECT subquery.*, orders_log.ol_user
FROM orders_log main
JOIN
(
SELECT orders.o_id, /* The remaining fields of orders go here */,
MAX(orders_log.ol_timestamp) as latest
FROM orders
NATURAL JOIN orders_log
GROUP BY orders.o_id, /* the remaining fields of orders go here */
) subquery
ON main.ol_timestamp = subquery.latest
AND main.o_id = subquery.o_id

----- Original Message -----
From: "Gary Stainburn" <gary(dot)stainburn(at)ringways(dot)co(dot)uk>
To: <pgsql-sql(at)postgresql(dot)org>
Sent: Monday, September 28, 2009 12:02 PM
Subject: Re: [SQL] simple (?) join

On Saturday 26 September 2009 21:15:37 justin wrote:
> David W Noon wrote:
> On Sat, 26 Sep 2009 14:54:24 -0400, justin wrote about Re: [SQL] simple
> (?) join:
>
> [snip]
>
> Quoting Gary
> "How can I select all from orders and the last (latest) entry from the
> orders_log?"
>
>
> In that case, a simple Cartesian product will do:
>
> SELECT o.*, maxi.ts
> FROM orders AS o,
> (SELECT MAX(ol_timestamp) AS ts FROM orders_log) AS maxi;
>
> Since the cardinality of the subquery "maxi" is 1, it will give a result
> set with cardinality of the complete orders table.
>
> I don't understand why anybody would want to do that. [De gustibus ... ]
>
>
> Guessing here
>
> Answer to return the last time someone either viewed or edited the order.
>
> This is a very common audit requirement to track who what, when and why
> something happened.

For some reason the reply I sent on Friday didn't get through.
What I need is all of the order record and all of the latest log entry
returning as a join. Specifically I want for each order the most recent log
entry timestamp and it's associated user - i.e. who made the the last log
entry and when.

I suppose I'm asking how I would do the sub-query to pull the most recent
log
entry per order.

--
Gary Stainburn

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