Re: BUG #17477: A crash bug in transformValuesClause()

On 5/9/22 11:25 AM, Tom Lane wrote:
> Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> writes:
>> It seems like transformValuesClause() cannot handle properly the value
>> clause having a relation that has an empty column. Should we raise an
>> error in this case?
>
> Given that we try to support zero-column relations, I'm not sure why
> we'd insist on disallowing zero-column VALUES. I think the problem
> is that the code in transformValuesClause needs to be tweaked to
> make that work. The attached quick hack seems to do the trick.

Agree with the reasoning.

Confirmed reproducing the crash and that this fixes it. I did a short
double-take on the error message:

ERROR: subquery must return only one column

but it is accurate, given this is what the subquery must do, and zero !=
one.

I don't see anything glaring in the code (though I'm not that familiar
with this part of the codebase), but given this seems like an extreme
edge case and protects against a crash, I'm satisfied with this.

Jonathan