Re: Assert failure in try_nestloop_path()

Richard Guo <guofenglinux(at)gmail(dot)com> 于2026年9月1日周二 15:43写道：
>
> I was studying the PHV bug caused by join-removal and ran into an
> assertion failure with the query below, which is not related to
> join-removal. So start a new thread for it.
>
> create table ta (id int primary key, x int);
> create table tb (id int primary key, a_id int, x int);
> create table tc (id int, x int);
>
> explain (costs off)
> select 1 from ta t1 left join
> (select tb.x as bx, 1 as one from ta a2 left join tb on a2.id =
> tb.a_id) t2 on true
> left join lateral (select tc.x as cnt from tc where tc.id = t2.one
> offset 0) t3
> on t2.bx = t3.cnt;
>
> TRAP: failed Assert("!have_unsafe_outer_join_ref(root, outerrelids,
> inner_paramrels)")
>

I tested v1 and it fixes the reported assertion failure.

I also noticed that the resulting plan contains a duplicated filter:
QUERY PLAN
-------------------------------------------------------------------
Nested Loop Left Join
-> Seq Scan on ta t1
-> Materialize
-> Nested Loop Left Join
-> Hash Right Join
Hash Cond: (tb.a_id = a2.id)
-> Seq Scan on tb
-> Hash
-> Seq Scan on ta a2
-> Subquery Scan on t3
Filter: ((tb.x = t3.cnt) AND (tb.x = t3.cnt))
-> Seq Scan on tc
Filter: (id = (1))

```
Filter: ((tb.x = t3.cnt) AND (tb.x = t3.cnt))
```

This is not introduced by v1; I can reproduce the same duplicate qual on
pg16.14 as well, so it seems to be a pre-existing issue.

It is probably unrelated to this fix, but I thought it was worth mentioning
since the test case exposes it.

--
Thanks,
Tender Wang