Re: Internal design of MERGE, with Rules

On Thu, 2008-05-01 at 00:26 +0100, Sam Mason wrote:

> On Wed, Apr 30, 2008 at 04:58:52PM +0100, Simon Riggs wrote:
> > That means we probably need to introduce new infrastructure in the tcop
> > or executor modules to handle queries-within-queries. This isn't
> > special-casing MERGE so much as introducing infrastructure for a new
> > class of query, such as MERGE, REPLACE, INSERT ELSE UPDATE. (Merge
> > itself does cover almost all cases of this type of query, but we'd be
> > able to fairly easily support all of the different syntax).
> >
> > MERGE would then be represented by a query that has many "side
> > queries" (so called so we don't confused calling them sub-queries).
>
> Why make them special cases? (I'm sure there's a good reason!)

Well, I'm not making them special cases. The infrastructure would be
generalised for any statement type that wanted to do roughly this.

> I've sometimes wanted to be able to put DML statements inside SELECT
> statements. The following is a slightly reasonable example:
>
> INSERT INTO ilog (i,ts,n)
> SELECT i, now(), COUNT(*)
> FROM (
> INSERT INTO bar (x,y)
> SELECT 5, n
> FROM baz
> WHERE i = 10
> RETURNING i) x
> GROUP BY i;

OK, but that's not what I'm working on... useful as it sounds.

--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com