Re: inequality predicate not pushed down in JOIN?

Cool! Thanks for the speedy reply, link, and summary! I'm not sure how I
missed this, but apologies for the noise.

-Paul-

On Thu, Jul 11, 2024 at 4:49 PM Andrei Lepikhov <lepihov(at)gmail(dot)com> wrote:

> On 12/7/2024 06:31, Paul George wrote:
> > In the example below, I noticed that the JOIN predicate "t1.a<1" is not
> > pushed down to the scan over "t2", though it superficially seems like it
> > should be.
> It has already discussed at least couple of years ago, see [1].
> Summarising, it is more complicated when equivalences and wastes CPU
> cycles more probably than helps.
>
> >
> > create table t as (select 1 a);
> > analyze t;
> > explain (costs off) select * from t t1 join t t2 on t1.a=t2.a and t1.a<1;
> > QUERY PLAN
> > -------------------------------
> > Hash Join
> > Hash Cond: (t2.a = t1.a)
> > -> Seq Scan on t t2
> > -> Hash
> > -> Seq Scan on t t1
> > Filter: (a < 1)
> > (6 rows)
> >
> > The same is true for the predicate "t1.a in (0, 1)". For comparison, the
> > predicate "t1.a=1" does get pushed down to both scans.
> >
> > explain (costs off) select * from t t1 join t t2 on t1.a=t2.a and t1.a=1;
> > QUERY PLAN
> > -------------------------
> > Nested Loop
> > -> Seq Scan on t t1
> > Filter: (a = 1)
> > -> Seq Scan on t t2
> > Filter: (a = 1)
> > (5 rows)
>
> [1] Condition pushdown: why (=) is pushed down into join, but BETWEEN or
> >= is not?
>
> https://www.postgresql.org/message-id/flat/CAFQUnFhqkWuPCwQ1NmHYrisHJhYx4DoJak-dV%2BFcjyY6scooYA%40mail.gmail.com
>
> --
> regards, Andrei Lepikhov
>
>