Re: BUG #18184: ERROR: wrong varnullingrels (b) (expected (b 3)) for Var 2/2

On Mon, Nov 6, 2023 at 10:39 PM PG Bug reporting form <
noreply(at)postgresql(dot)org> wrote:

> Hi,
> We found a bug in PostgreSQL 16. I have simplified the case:
>
> SELECT
> function1(table1)
> FROM table2
> LEFT JOIN table1 ON table1_id = table2_id
> LEFT JOIN LATERAL (SELECT 1 FROM table3) AS tx3 ON (true)
> LIMIT 5;
>
> ERROR: wrong varnullingrels (b) (expected (b 3)) for Var 2/2

Thanks for the report! This is an error message that hasn't been seen
in a long time.

It seems that when we optimize field selection from a whole-row Var into
a simple Var while simplifying functions, we fail to propagate the
nullingrels into the new Var.

Attached is a hotfix for this error. But I'm wondering if there are
other similar cases where we have mismatched nullingrels that we haven't
discovered yet. Any thoughts?

Thanks
Richard