Re: BUG #18634: Wrong varnullingrels with merge ... when not matched by source

PG Bug reporting form  writes:
> The following script:
> CREATE TABLE t (a int);
> INSERT INTO t VALUES(1), (2);
> CREATE VIEW v AS SELECT a FROM t WHERE EXISTS (SELECT 1 FROM t);

> MERGE INTO v USING (SELECT * FROM generate_series(1,1)) AS s(a)
>   ON s.a = v.a WHEN NOT MATCHED BY SOURCE THEN DELETE;

> produces:
> ERROR:  XX000: wrong varnullingrels (b) (expected (b 4)) for Var 5/1
> LOCATION:  search_indexed_tlist_for_var, setrefs.c:2847

I haven't run this fully to ground, but what it looks like
is that preprocess_targetlist is generating row identity
Vars that lack required varnullingrels.  I don't understand
though why this only seems to affect MERGE.

			regards, tom lane