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From: Kev <kevinjamesfield(at)gmail(dot)com>
To: pgsql-patches(at)postgresql(dot)org
Subject: Re: WITH RECURSIVE patch V0.1
Date: 2008-05-20 14:03:16
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackerspgsql-patches
On May 19, 1:17 am, da(dot)(dot)(dot)(at)fetter(dot)org (David Fetter) wrote:
> On Mon, May 19, 2008 at 12:21:20AM -0400, Gregory Stark wrote:
> > It's quite possible to have clauses which will limit the output but
> > not in a way the database can determine.  Consider for example a
> > tree-traversal for a binary tree stored in a recursive table
> > reference.  The DBA might know that the data contains no loops but
> > the database doesn't.
> I seem to recall Oracle's implementation can do this traversal on
> write operations, but maybe that's just their marketing.

That's how I implement (id, name, parent)-trees as a DBA, having an
insert/update trigger function check_no_loops(), but I'm not sure that
it would be faster than the hash method suggested by Hannu Krosing.  I
guess it depends on whether you're inserting/updating or selecting
more.  Does it make sense to leave the option to the user, whether to
check for infinite recursion just in time or not?


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