Re: inequality predicate not pushed down in JOIN?

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