Re: MERGE Specification

On Thu, Aug 05, 2010 at 09:55:29PM +0800, Boxuan Zhai wrote:
> On Thu, Aug 5, 2010 at 7:25 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> 
> > On Thu, 2010-08-05 at 12:29 +0300, Heikki Linnakangas wrote:
> > > On 05/08/10 10:46, Simon Riggs wrote:
> > > > On Mon, 2008-04-21 at 21:08 +0100, Simon Riggs wrote:
> > > >> The following two files specify the behaviour of the MERGE statement
> > and
> > > >> how it will work in the world of PostgreSQL.
> > > >
> > > >> The HTML file was generated from SGML source, though the latter is not
> > > >> included here for clarity.
> > > >
> > > > Enclose merge.sgml docs for forthcoming MERGE command, as originally
> > > > written.
> > >
> > > Oh, cool, I wasn't aware you had written that already. Boxuan, please
> > > include this in your patch, after reviewing and removing/editing
> > > anything that doesn't apply to your patch.
> >
> Thanks a lot for the instruction file of MERGE command. I have read through
> it carefully. It is really a great work. I have to admit that I am not
> familiar with the sgml language, and I cannot write the instruction by
> myself.

It's really not super complicated.  It's quite like (and ancestral to)
HTML.

> All features of MERGE demonstrated in this file are consistent with my
> implementation, EXCEPT the DO NOTHING option. In current edition, we don't
> have the DO NOTHING action type. That is, during the execution of MERGE
> commands, if one tuple is not caught by any of the merge actions, it will be
> ignored. In another word, DO NOTING (although cannot be specified explicitly
> by user) is the DEFAULT action for tuples.
> 
> In the contrary, Simon's instruction says that the DEFAULT action for the
> tuple caught by no actions is
> WHEN NOT MATCHED THEN INSERT DEFAULT VALUES

I believe that the SQL standard specifies this behavior, and I don't
think we have a compelling reason to do something different from what
the SQL standard specifies.

> Well, if people want the DO NOTHING action, I will add it in the system.

That'd be great :)

>  Now, I have changed the RULE strategy of MERGE to the better logic. And I
> am working on triggers for MERGE, which is also mentioned in the instruction
> file. I will build a new patch with no long comment and blank line around
> functions, and possibly contain the regress test file and this sgml
> instructions in it.
> 
> I wish we can reach a agreement on the DO NOTHING thing before my next
> submission, so I can make necessary modification on my code for it. (the new
> patch may be finished in one or two days, I think)
> 
> Thanks!
> 
> PS: I have an embarrassing question: how to view the sgml instructions of
> postgres in web page form, rather than read the source code of them?

After you've built postgresql, do this:

cd doc/src/sgml
make

Then you can point a web browser at the doc/src/sgml/html/index.html
(and similar)

http://www.postgresql.org/docs/current/static/docguide.html

has information about the tools you will need for the above to work.

Cheers,
David.
-- 
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david.fetter@gmail.com
iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate