pg.ddx.io  pgsql-hackers@postgresql.org mailing list archive  

help / color / mirror / Atom feed
From: srielau <serge@rielau.com>
To: pgsql-hackers@postgresql.org
Subject: Re: MERGE SQL Statement for PG11
Date: Fri, 27 Oct 2017 14:13:27 -0700 (MST)
Message-ID: <1509138807748-0.post@n3.nabble.com> (raw)
In-Reply-To: <CA+TgmobMx66NWCoje=PEGnbMQQdZojJi7v9RqsuY23vkNsTf1Q@mail.gmail.com>
References: <CANP8+jKitBSrB7oTgT9CY2i1ObfOt36z0XMraQc+Xrz8QB0nXA@mail.gmail.com>
	<CA+TgmoZuce2iHSBVpkX5qud-UbxhtY85opA47LTP=QW16J47wg@mail.gmail.com>
	<CANP8+j+jG76Okkibk7Xu=T6C5-gSpXX9sudANS9nGyR9yWEgRA@mail.gmail.com>
	<CA+TgmobMx66NWCoje=PEGnbMQQdZojJi7v9RqsuY23vkNsTf1Q@mail.gmail.com>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-hackers>

Simon,

Nice writeup.

While the standard may not require a unique index for the ON clause I have
never seen a MERGE statement that did not have this property.  So IMHO this
is a reasonable restrictions.

In fact I have only ever seen two flavors of usage:
* Single row source (most often simply a VALUES clause) in OLTP
  In that case there was lots of concurrency
* Massive source which affects a significant portion of the target table in
DW.
 In this case there were no concurrent MERGEs

I believe support for returning rows at a later stage would prove to be very
powerful, especially in combination with chaining MERGE statements in CTEs.
To do that would require language extensions to pass the coloring of the
source row through, especially for rows that fell into "do nothing".




--
Sent from: http://www.postgresql-archive.org/PostgreSQL-hackers-f1928748.html


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers



view thread (265+ messages)  latest in thread

Message-ID: <1509138807748-0.post@n3.nabble.com>
Permalink:  ../1509138807748-0.post@n3.nabble.com/
Also on:    postgresql.org/message-id/1509138807748-0.post@n3.nabble.com

 · 

reply
Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: pgsql-hackers@postgresql.org
  Cc: serge@rielau.com
  Subject: Re: MERGE SQL Statement for PG11
  In-Reply-To: <1509138807748-0.post@n3.nabble.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox