Re: ERROR: wrong varnullingrels (b 3) (expected (b)) for Var 2/1

On Tue, May 30, 2023 at 10:48 PM Markus Winand <markus.winand@winand.at>
wrote:

> I found an error similar to others before ([1]) that is still persists as
> of head right now (0bcb3ca3b9).
>
> CREATE TABLE t (
>         n INTEGER
> );
>
> SELECT *
>   FROM (VALUES (1)) t(c)
>   LEFT JOIN t ljl1 ON true
>   LEFT JOIN LATERAL (WITH cte AS (SELECT * FROM t WHERE t.n = ljl1.n)
> SELECT * FROM cte) ljl2 ON ljl1.n = 1;
>
> ERROR:  wrong varnullingrels (b 3) (expected (b)) for Var 2/1
>
> Note that the error does **not** occur if the CTE is unwrapped like this:
>
> SELECT *
>   FROM (VALUES (1)) t(c)
>   LEFT JOIN t ljl1 ON true
>   LEFT JOIN LATERAL (SELECT * FROM t WHERE t.n = ljl1.n) ljl2 ON ljl1.n =
> 1;


Thanks for the report!  Reproduced here.  Also it can be reproduced with
subquery, as long as the subquery is not pulled up.

SELECT *
  FROM (VALUES (1)) t(c)
  LEFT JOIN t ljl1 ON true
  LEFT JOIN LATERAL (SELECT * FROM t WHERE t.n = ljl1.n offset 0) ljl2 ON
ljl1.n = 1;
ERROR:  wrong varnullingrels (b 3) (expected (b)) for Var 2/1

When we transform the first form of identity 3 to the second form, we've
converted Pb*c to Pbc in deconstruct_distribute_oj_quals.  But we
neglect to consider that rel C might be a RTE_SUBQUERY and contains
quals that have lateral references to B.  So the B vars in such quals
have wrong nulling bitmaps and we'd finally notice that when we do
fix_upper_expr for the NestLoopParam expressions.

Thanks
Richard