Re: Guidance on INSERT RETURNING order

Sorry, I may have jumped to a conclusion that's not quite correct.

On Mon, 17 Apr 2023 at 23:58, Federico <cfederico87(at)gmail(dot)com> wrote:

> On Tue, 18 Apr 2023 at 00:21, John Howroyd <jdhowroyd(at)googlemail(dot)com>
> wrote:
> > ...
> >
> > Personally, I didn't see Frederico's comment as anything to do with
> order; just how one could output additional values in the RETURNING clause
> (namely, v.num from a subexpression of the SELECT but in whatever order it
> comes). On the other hand, that seems a lot more complicated to me because
> it is not an expression in the overall SELECT feeding the INSERT, whereas
> the WITH ORDINALITY is a specific declaration to match input order with
> output order by inserting a counter.
>
> I didn't mean to suggest any particular order should be kept by insert
> or by returning. I was merely commenting on the David G. Johnston
> reply
>
> I suppose breaking the restriction that only columns present on
> the insertion-table can be returned is a possible option that also
> solves another infrequent request.
>
>
...
> Best,
> Federico
>

This might be a possibility. The v.num (from the original example) is
accessible in the outer select, so one can a envisage a system to handle
this, but at (presumably) much greater expense: preparation of the SELECT,
orchestration of the output rows (some fields for INSERT some for
RETURNING) and (presumably) a whole load of mem copies to RETURNING. Is
this something to consider (perhaps just for feasibility while writing an
initial patch based on WITH ORDINALITY)?

To put it another way, v.num is a valid expression in the overall SELECT,
but still a lot more complicated (and presumably expensive).