Need help with a query

From: A B <gentosaker(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: Need help with a query
Date: 2010-10-26 09:16:58
Message-ID: AANLkTi=iWg+qLHMh7PBQjx17Qi+7DmSVK1pPZeVt0=OV@mail.gmail.com
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Hello.

I'm having a problem with a probably very simple query.
I need to update a table
foo (x int, y int, last_seen timestamp, unique(x,y));

where the values should be taken from a larger table
bar( x int, y int, seen timestamp);
where each x,y combination occurs several times, and the value in
foo.last_seen should be the value max(seen) for each pair of x,y.
Notice! All combinations of x,y in bar are also in foo, but not the
other way around.

So how do I write a query for this?
Thanks in advance.

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