Re: 7.4 Wishlist

On Tue, 2002-12-03 at 16:00, Bruce Momjian wrote:
> Is WITH a TODO item?

It is disguised as

Exotic Features
===============

* Add sql3 recursive unions

Which was added at my request in dark times, possibly when PostgreSQL
was called postgres95 ;)

This should be changed to two items

* Add SQL99 WITH clause to SELECT

* Add SQL99 WITH RECURSIVE to SELECT

> ---------------------------------------------------------------------------
>
> Hannu Krosing wrote:
> > On Tue, 2002-12-03 at 09:20, Dennis Bj?rklund wrote:
> > > On Tue, 3 Dec 2002, Magnus Naeslund(f) wrote:
> > >
> > > > Now convert this query so that it only evaluates the date_part thing
> > > > ONCE:
> > > >
> > > > select t.id, date_part('days',now()-t.stamp) from table_name t where
> > > > date_part('days',now()-t.stamp) > 20;
> > >
> > > Something like this could work:
> > >
> > > select *
> > > from (select t.id, date_part('days',now()-t.stamp) AS d
> > > from table_name t) AS t1
> > > where t1.d > 20;
> > >
> > > That aside I also would like some sort of local names. Something like the
> > > let construct used in many functional languages (not exaclty what you want
> > > above, but still):
> > >
> > > let t1 = select * from foo;
> > > t2 = select * from bar;
> > > in select * from t1 natural join t2;
> > >
> > > But even though I would like to give name to subexpressions like above, I
> > > still think postgresql should stick to standards as close as possible.
> >
> > the standard way of doing it would be SQL99's WITH :
> >
> > with t1 as (select * from foo)
> > t2 as (select * from bar)
> > select * from t1 natural join t2;
> >
> > you can even use preceeding queries
> >
> > with t1 as (select a,b from foo)
> > t1less as (select a,b from t1 where a < 0)
> > t1zero as (select a,b from t1 where a = 0)
> > select * from t1zero, t1less, where t1zero.b = t1less.a;
> >
> > Having working WITH clause is also a prerequisite to implementing SQL99
> > recursive queries (where each query in WITH clause sees all other
> > queries in the WITH clause)
> >
> > I sent a patch to this list recently that implements the above syntax,
> > but I currently dont have knowledge (nor time to aquire it), so if
> > someone else does not do it it will have to wait until January.
> >
> > OTOH, I think that turning my parsetree to a plan would be quite easy
> > for someone familiar with turning parestrees into plans ;)
> >
> > I offer to check if it works in current (and make it work again if it
> > does not) if someone would be willing to hold my hand in implementation
> > parsetree-->plan part ;).
> >
> > I think that for non-recursive queries this is all that needs to be
> > done, i.e. the plan would not care if the subqueries were from FROM,
> > from WITH or from separately defined views.
> >
> > --
> > Hannu Krosing <hannu(at)tm(dot)ee>
> >
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--
Hannu Krosing <hannu(at)tm(dot)ee>