Received: from malur.postgresql.org ([217.196.149.56])
	by arkaria.postgresql.org with esmtps
 (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <pgsql-hackers-owner+archive@lists.postgresql.org>)
	id 1jbOOh-0003Qv-82
	for pgsql-hackers@arkaria.postgresql.org; Wed, 20 May 2020 13:04:35 +0000
Received: from localhost ([127.0.0.1] helo=malur.postgresql.org)
	by malur.postgresql.org with esmtp (Exim 4.92)
	(envelope-from <pgsql-hackers-owner+archive@lists.postgresql.org>)
	id 1jbOOg-0007hI-3d
	for pgsql-hackers@arkaria.postgresql.org; Wed, 20 May 2020 13:04:34 +0000
Received: from makus.postgresql.org ([2001:4800:3e1:1::229])
	by malur.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <vik@postgresfriends.org>)
	id 1jbOOf-0007hB-Td
	for pgsql-hackers@lists.postgresql.org; Wed, 20 May 2020 13:04:33 +0000
Received: from relay4-d.mail.gandi.net ([217.70.183.196])
	by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <vik@postgresfriends.org>)
	id 1jbOOY-0003Df-CR
	for pgsql-hackers@postgresql.org; Wed, 20 May 2020 13:04:32 +0000
X-Originating-IP: 93.10.30.82
Received: from [172.16.255.146] (82.30.10.93.rev.sfr.net [93.10.30.82])
	(Authenticated sender: vik@postgresfriends.org)
	by relay4-d.mail.gandi.net (Postfix) with ESMTPSA id B2EA8E0016;
	Wed, 20 May 2020 13:04:21 +0000 (UTC)
Subject: Re: SEARCH and CYCLE clauses
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
References: <db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com>
From: Vik Fearing <vik@postgresfriends.org>
Message-ID: <54e533c5-09e5-7f41-9892-d4e0f7c62598@postgresfriends.org>
Date: Wed, 20 May 2020 15:04:20 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
List-Id: <pgsql-hackers.lists.postgresql.org>
List-Help: <https://lists.postgresql.org/manage/>
List-Subscribe: <https://lists.postgresql.org/manage/>
List-Post: <mailto:pgsql-hackers@lists.postgresql.org>
List-Owner: <mailto:pgsql-hackers-owner@lists.postgresql.org>
List-Archive: <https://www.postgresql.org/list/pgsql-hackers>
Precedence: bulk

On 5/20/20 1:46 PM, Peter Eisentraut wrote:
> I have implemented the SEARCH and CYCLE clauses.

YES!

> This is standard SQL syntax attached to a recursive CTE to compute a
> depth- or breadth-first ordering and cycle detection, respectively. This
> is just convenience syntax for what you can already do manually. The
> original discussion about recursive CTEs briefly mentioned these as
> something to do later but then it was never mentioned again.
> 
> SQL specifies these in terms of syntactic transformations, and so that's
> how I have implemented them also, mainly in the rewriter.

I've attempted to do this several times but didn't get anywhere with it.
 I'm looking forward to reviewing this.

(And maybe it will put me on the right path for implementing <unique
predicate>.)
-- 
Vik Fearing