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From: Tom Lane <[email protected]>
To: Alvaro Herrera <[email protected]>
Cc: Pg Hackers <[email protected]>
Subject: Re: "variable not found in subplan target list"
Date: Tue, 28 Mar 2023 09:17:00 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

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

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