Re: Early WIP/PoC for inlining CTEs

Hi,

On 2019-01-12 07:58:39 +1300, Thomas Munro wrote:
> On Sat, Jan 12, 2019 at 7:19 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On 2019-01-11 11:12:25 -0500, Robert Haas wrote:
> > > I actually think that we should go "all in" here and allow the user to
> > > specify either that they want materialization or that they don't want
> > > materialization. If they specify neither, then we make some decision
> > > which we may change in a future release. If they do specify
> > > something, we do that.
> >
> > +many
>
> I think the syntax as proposed is almost OK if we only want to
> grandfather in our historically hintful CTEs but discourage the
> development of any future kinds of hints. Even then I don't love the
> way it formalises a semi-procedural step at the same language level as
> a glorious declarative relational query.
>
> Maybe we could consider a more extensible syntax that is attached to
> the contained SELECT rather than the containing WITH. Then CTEs would
> be less special; there'd be a place to put hints controlling top-level
> queries, subselects, views etc too (perhaps eventually join hints,
> parallelism hints etc, but "materialize this" would be just another
> one of those things). That'd be all-in.

I think you have some purity arguments here, but the likelihood of us
developing a full-blown solution is not that high, and the lack of
inlinable CTEs is *really* hurting us. As long as the design doesn't
block a full solution, if we go there, I think it's a very acceptable
blemish in comparison to the benefits we'd get.

Greetings,

Andres Freund