Re: "variable not found in subplan target list"

I wrote:
> I reduced this down to

> MERGE INTO public.target_parted as target_0
>     USING public.itest1 as ref_0
>     ON target_0.b = ref_0.a
>     WHEN NOT MATCHED
>        THEN INSERT VALUES (42, 13);

> The critical moving part seems to just be that the MERGE target
> is a partitioned table ... but surely somebody tested that before?

Oh, it's not just any partitioned table:

regression=# \d+ target_parted
                                Partitioned table "public.target_parted"
 Column |  Type   | Collation | Nullable | Default | Storage | Compression | Stats target | Description
--------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
 a      | integer |           |          |         | plain   |             |              |
 b      | integer |           |          |         | plain   |             |              |
Partition key: LIST (a)
Number of partitions: 0

The planner is reducing the scan of target_parted to
a dummy scan, as is reasonable, but it forgets to
provide ctid as an output from that scan; then the
parent join node is unhappy because it does have
a ctid output.  So it looks like the problem is some
shortcut we take while creating the dummy scan.

I suppose that without the planner bug, this'd fail at
runtime for lack of a partition to put (42,13) into.
Because of that, the case isn't really interesting
for production, which may explain the lack of reports.

            regards, tom lane