Re: [HACKERS] Re: [SQL] cursor and update + view

Jan Wieck wrote:
>
> > rule system will be able to put _any_ VIEW' query into
> > FROM clause...
>
>     Possible - but IMHO the wrong thing to do. As it is now for a

"Will be able" doesn't mean "will DO" -:))
I just said that subqueries in FROM will resolve all
problems with aggregates in VIEWs.

>     If  we put any view into a subquery RTE, we force the planner
>     to materialize the  view  and  do  a  nestloop  over  t3  and
         ^^^^^^^^^^^
Do you mean creating some tmp table etc?
No - it's not required.

>     materialized  v1  where  possibly  using  t1  or  t2  as  the
>     outermost scanrelation would be better.

  SELECT t3.a, v1.b, v1.c
  FROM t3,
       (SELECT t1.a, t1.b, t2.c FROM t1, t2 WHERE t1.a = t2.a) v1
  WHERE t3.a = v1.a;

can be planned as

    Nestloop
    SubPlan
           ...what is costless for subquery...
    Seq/Index scan on t3

- no materialization...

On the other hand, as we talk about query optimization - why
rule system should do optimizer' work? Why not just put
_any_ VIEW' query into FROM and let optimizer decide
could query be rewritten as join or not? Ppl do strange
things sometimes -:) Sometimes they use subqueries in
WHERE while joins could be used and our optimizer don't
try to catch this. I know that Sybase does.
And, imho, we should implement this ... sometime -:))

Vadim