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Date: Sat, 03 Jan 2004 03:20:46 -0600
From: John Coryat <john@coryat.com>
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To: pgsql-sql@postgresql.org
Subject: Complex Update
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Problem: I have a table that has a field I want to plug with a value 
from other tables.

I can do it with a perl program and a loop, but want to do it with a 
single SQL statement.

Is there a way to do an update that combines a select statement 
containing a "where" that uses a field from the row to be updated?

I would expect it to look something like this:

update orderheader set total = (select sum(amount) from orderdetail 
where orderdetail.orderno=orderheader.orderno) ;

Any ideas?