Re: BUG #19534: Qual pushdown across a window subquery is unsafe with nondeterministic partition collations

PG Bug reporting form <noreply(at)postgresql(dot)org> 于2026年6月27日周六 20:55写道：
>
> The following bug has been logged on the website:
>
> Bug reference: 19534
> Logged by: Qifan Liu
> Email address: imchifan(at)163(dot)com
> PostgreSQL version: 18.4
> Operating system: Ubuntu 20.04 x86-64, docker image postgres:18.4
> Description:
>
> ## Expected Behavior
>
> The window query should return the same result as the reference query. Since
> `'abc'` and `'ABC'` are in the same nondeterministic partition, the
> partition sum for row `'abc'` should be `3`.
>
> ## Actual Behavior
>
> The window query returns `abc | 1 | 1`, while the reference query returns
> `abc | 1 | 3`. `EXPLAIN` shows that the strict-collation filter is pushed
> below `WindowAgg`, which changes the partition before the window sum is
> computed.
>

Yes, I can reproduce this on HEAD.
The whereClause was pushed down to the scan level of table t_window_ci.
So the row with 'ABC' was ignored by the filter.

In current logic, we have no logic to process a nondeterministic
partition clause when considering whether the
qual can be pushed down to the subquery.

I try to fix this with the attached patch.
I add a new flag UNSAFE_HAS_NONDETERMINITIC for
pushdown_safety_info.unsafeFlags.
If the var is in the partition clause and it is nondeterministic, we
set this flag.
In qual_is_pushdown_safe(), we check the qual's inputcollid; if it is
deterministic, but the var in
the partition clause is nondeterministic, it is PUSHDOWN_UNSAFE.

Any thoughts?
--
Thanks,
Tender Wang