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Date: Sat, 4 Apr 2026 23:52:02 +0200
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Subject: Re: TupleDescAttr bounds checks
To: Tom Lane <tgl@sss.pgh.pa.us>, Alexander Lakhin <exclusion@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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From: Peter Eisentraut <peter@eisentraut.org>
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On 04.04.26 17:38, Tom Lane wrote:
> I wrote:
>> But I bet this loop should throw an error for system columns, too,
>> since we surely won't have computed those either.
> 
> After poking at that: testing tableoid does sort of work, in that it
> reads as the OID of the target table named in COPY.  But I think any
> rational use for a test on tableoid here would be in connection with
> a partitioned target table, and the user would wish it to read as the
> OID of the destination partition.  So I think we should disallow
> tableoid along with the other system columns, pending somebody having
> the ambition to make that work.
> 
> So I propose the attached for HEAD.  (I couldn't resist the temptation
> to clean up adjacent comments.)  In the back branches it might be
> better to just ignore system columns here, on the tiny chance that
> somebody thinks they do something useful.

I think this is the same issue that was discussed here:

https://www.postgresql.org/message-id/flat/30c39ee8-bb11-4b8f-9697-45f7e018a8d3%40eisentraut.org

There was no conclusion there, but I agree with the proposal to prohibit 
this use.