Re: ERROR: wrong varnullingrels (b 3) (expected (b)) for Var 2/1 - Mailing list pgsql-hackers

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.