Re: simple (?) join

From: justin <justin(at)emproshunts(dot)com>
To: David W Noon <dwnoon(at)ntlworld(dot)com>, pgsql-sql(at)postgresql(dot)org
Subject: Re: simple (?) join
Date: 2009-09-26 20:15:37
Message-ID: 4ABE7669.50001@emproshunts.com
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David W Noon wrote:
<blockquote cite="mid:20090926205349(dot)5fa284f1(at)dwnoon(dot)ntlworld(dot)com"
type="cite">
<pre wrap="">On Sat, 26 Sep 2009 14:54:24 -0400, justin wrote about Re: [SQL] simple
(?) join:

[snip]
</pre>
<blockquote type="cite">
<pre wrap="">Quoting Gary
"How can I select all from orders and the last (latest) entry from the
orders_log?"
</pre>
</blockquote>
<pre wrap=""><!---->
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 ... ]
</pre>
</blockquote>
<br>
Guessing here <br>
<br>
&nbsp;Answer to return the last time someone either viewed or edited the
order.<br>
<br>
This is a very common audit requirement to track who what, when and why
something happened.&nbsp; <br>
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