SQL/MED spec for cross-database linkages

Joe, have you heard of a standard called SQL/MED? I came across a
description of it the other day. You might think it's got some medical
connotation, but actually the acronym is Management of External Data,
and what it is is a standard spec for shipping chunks of SQL queries to
remote servers. For instance, given

SELECT * FROM a.foo, b.bar WHERE ...

where a.foo is on a remote machine, the spec lays down how the local and
remote servers can cooperate to execute this query intelligently ---
including deciding where to execute various WHERE clauses to minimize
the amount of data shipped. (The article I found was actually about
how the new draft version of SQL/MED improves the protocol to let this
sort of thing be done better; it seems the original spec only allowed
retrieval of a whole table's contents.)

This looks like it might be a great long-term replacement for dblink,
and if it is standard, so much the better.

I imagine the draft version of the new SQL/MED spec may be available on
the web, but haven't gone looking.

Just a heads-up in case you are interested...

regards, tom lane

On Fri, 2002-12-06 at 11:04, Tom Lane wrote:
> Joe, have you heard of a standard called SQL/MED? I came across a

It's that one of the later parts of the SQL 99 spec? Section 9 or
thereabouts?

--
Rod Taylor <rbt(at)rbt(dot)ca>

PGP Key: http://www.rbt.ca/rbtpub.asc

On Fri, 2002-12-06 at 11:35, Rod Taylor wrote:
> On Fri, 2002-12-06 at 11:04, Tom Lane wrote:
> > Joe, have you heard of a standard called SQL/MED? I came across a
>
> It's that one of the later parts of the SQL 99 spec? Section 9 or
> thereabouts?

Note to self, don't reply to emails and have a separate conversation at
the same time.

Found SQL/MED, Section 21 of ISO 9075-9.

--
Rod Taylor <rbt(at)rbt(dot)ca>

PGP Key: http://www.rbt.ca/rbtpub.asc

Tom Lane wrote:
> Joe, have you heard of a standard called SQL/MED? I came across a
> description of it the other day. You might think it's got some medical
> connotation, but actually the acronym is Management of External Data,
> and what it is is a standard spec for shipping chunks of SQL queries to
> remote servers. For instance, given
>
> SELECT * FROM a.foo, b.bar WHERE ...
>
> where a.foo is on a remote machine, the spec lays down how the local and
> remote servers can cooperate to execute this query intelligently ---
> including deciding where to execute various WHERE clauses to minimize
> the amount of data shipped. (The article I found was actually about
> how the new draft version of SQL/MED improves the protocol to let this
> sort of thing be done better; it seems the original spec only allowed
> retrieval of a whole table's contents.)
>
> This looks like it might be a great long-term replacement for dblink,
> and if it is standard, so much the better.

Great! Thanks for the heads up. I see that Rod provided the reference in his
post -- I'll go find it.

The idea of expanding dblink to other RDBMSs is picking up steam. I've been
conversing off list with someone who has a semi-working hacked version of
dblink that uses JDBC in place of libpq.

Do you think a proposal based on the SQL/MED spec would be entertained for
7.4, or would the release after be a safer bet? I'm not sure (since I haven't
seen it yet) what I'm getting myself into ;-), but I might like to take it on
since there seems to be a lot of interest.

Joe

Joe

Rod Taylor <rbt(at)rbt(dot)ca> writes:
> Found SQL/MED, Section 21 of ISO 9075-9.

That's the old version, though. The new draft is at (digs out article)
http://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-14-XML-2002-03.pdf
according to this article, but I'm not having any luck accessing that
URL. Let me email the authors and see if I can get a copy.

regards, tom lane

Joe Conway <mail(at)joeconway(dot)com> writes:
> Do you think a proposal based on the SQL/MED spec would be entertained for
> 7.4, or would the release after be a safer bet?

The impression I get from this article is that SQL/MED is nontrivial.
If you think you can get something useful going for 7.4, step right up
--- but I think you should plan on being at it for awhile. In any
case, a multi-step implementation plan would be a good idea.

regards, tom lane

On Fri, Dec 06, 2002 at 01:52:01PM -0500, Tom Lane wrote:
> Rod Taylor <rbt(at)rbt(dot)ca> writes:
> > Found SQL/MED, Section 21 of ISO 9075-9.
>
> That's the old version, though. The new draft is at (digs out article)
> http://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-14-XML-2002-03.pdf
> according to this article, but I'm not having any luck accessing that
> URL. Let me email the authors and see if I can get a copy.

Hmm, seems you need to change protocols:

ftp://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-14-XML-2002-03.pdf

Ross

On Fri, Dec 06, 2002 at 01:52:01PM -0500, Tom Lane wrote:
> Rod Taylor <rbt(at)rbt(dot)ca> writes:
> > Found SQL/MED, Section 21 of ISO 9075-9.
>
> That's the old version, though. The new draft is at (digs out article)
> http://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-14-XML-2002-03.pdf
> according to this article, but I'm not having any luck accessing that
> URL. Let me email the authors and see if I can get a copy.
>
> regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: Have you searched our list archives?

Having pulled that one, I discover it's actually the XML related spec. The
MED one is at:

ftp://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-09-MED-2002-01.pdf

There's a text version, as well (always nice for grepping):

ftp://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-09-MED-2002-01.txt

Ross

"Ross J. Reedstrom" <reedstrm(at)rice(dot)edu> writes:
> Having pulled that one, I discover it's actually the XML related spec. The
> MED one is at:

> ftp://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-09-MED-2002-01.pdf

Ah-hah, so the URL in the SIGMOD Record article is just wrong :-(

Meanwhile, one of the authors sent me a copy privately (it helps to have
shared an office at grad school ;-)) which I was about to offer around,
but I guess we can just use the FTP link instead.

regards, tom lane