Re: [HACKERS] Partial fix for INSERT...SELECT problems

Tom Lane wrote:

>
> I have committed some fixes that prevent resjunk targets from being
> assigned to output columns in an INSERT/SELECT. This partially fixes
> the problem Michael Davis reported a few weeks ago. However, there's
> still a bug with confusion about column names. Given
>
> create table foo (a int4, b int4);
> CREATE
> create table bar (c int4, d int4);
> CREATE
>
> we can do
>
> select c, sum(d) from bar group by c;
>
> but not
>
> insert into foo select c, sum(d) from bar group by c;
> ERROR: Illegal use of aggregates or non-group column in target list
>
> The problem here is that the target expressions of the select have
> been relabeled with foo's column names before GROUP BY is processed.
> If you refer to them by the output column names then it works:
>
> insert into foo select c, sum(d) from bar group by a;
> INSERT 279412 1
>
> You can think of the query as having been rewritten to
>
> insert into foo select c AS a, sum(d) AS b from bar group by a;
>
> in which case the behavior makes some kind of sense. However,
> I think that this behavior is neither intuitive nor in conformance
> with SQL92's scoping rules. As far as I can tell, the definition
> of the result of "select c, sum(d) from bar group by c" is independent
> of whether it is inside an INSERT or not.
>
> Fixing this appears to require a substantial rearrangement of code
> inside the parser, which I'm real hesitant to do with only a week to go
> till 6.5 release. I propose leaving this issue on the "to fix" list for
> 6.6. Comments?

Does it really require that substantial rearrangement? Looks
to me that the renaming of the target columns is only done a
little too early. Could the per Query unique ID
Resno.resgroupref <-> GroupClause.tleGroupref help here?

I wonder if the renaming of the target columns during parse
is required at all. I think in the case of an INSERT this is
done allways in the planner again at preprocess_targetlist().

I agree that changing it that close to release isn't a good
idea, but we should move this item to the top ten of TODO
after v6.5.

Jan

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