Re: Unnecessary lateral dependencies implied by PHVs

Hi Richard:

On Mon, Oct 10, 2022 at 10:35 AM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:

> ... I'm asking because
> PHVs may imply lateral dependencies which may make us have to use
> nestloop join.
>

I thought lateral join imply nestloop join, am I missing something? Here
is my simple
testing.

postgres=# explain (costs off) select * from r1 join lateral (select r1.a
from r2) on true;
QUERY PLAN
----------------------------
Nested Loop
-> Seq Scan on r1
-> Materialize
-> Seq Scan on r2
(4 rows)

Time: 0.349 ms
postgres=# set enable_nestloop to off;
SET
Time: 0.123 ms

postgres=# explain (costs off) select * from r1 join lateral (select r1.a
from r2) on true;
QUERY PLAN
----------------------------
Nested Loop
-> Seq Scan on r1
-> Materialize
-> Seq Scan on r2
(4 rows)

--
Best Regards
Andy Fan