To: Jonathan Knopp <pgsql@delegated.net>
Cc: pgsql-sql@postgresql.org
Subject: Re: Way to stop recursion? 
In-reply-to: <41A79A2A.6070606@delegated.net> 
References: <41A79A2A.6070606@delegated.net>
Comments: In-reply-to Jonathan Knopp <pgsql@delegated.net>
	message dated "Fri, 26 Nov 2004 13:03:38 -0800"
Date: Fri, 26 Nov 2004 16:31:11 -0500
Message-ID: <19345.1101504671@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Jonathan Knopp <pgsql@delegated.net> writes:
> CREATE TABLE parent (id INT, cola CHAR(1), common CHAR(1));
> CREATE TABLE child (id INT, parent_id INT, cola(1), common(1));

> What I need, is when "common" is changed for a parent, then that new 
> value is reflected in "common" for all the children, ie:
> ...
> Problem is, when "common" is changed for a child, I need the parent and 
> all siblings to reflect that value too, ie:

Seems to me that your real problem is a bogus database layout.  If there
should only be one "common" value for a parent and children, then only
store one value ... that is, "common" should exist only in the parent.

You can if you like make a view that emulates the appearance of a child
table with a common column, viz

create view childview as select child.*, parent.common
  from child, parent where parent_id = parent.id;

and it would even be possible to make a rule that allows updating this
view.

			regards, tom lane