Re: MERGE ... RETURNING

On Tue, Oct 24, 2023 at 2:11 PM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:

> On Wed, 2023-08-23 at 11:58 +0100, Dean Rasheed wrote:
> > Updated version attached, fixing an uninitialized-variable warning
> > from the cfbot.
>
> I took another look and I'm still not comfortable with the special
> IsMergeSupportFunction() functions. I don't object necessarily -- if
> someone else wants to commit it, they can -- but I don't plan to commit
> it in this form.
>
> Can we revisit the idea of a per-WHEN RETURNING clause? The returning
> clauses could be treated kind of like a UNION, which makes sense
> because it really is a union of different results (the returned tuples
> from an INSERT are different than the returned tuples from a DELETE).
> You can just add constants to the target lists to distinguish which
> WHEN clause they came from.
>
> I know you rejected that approach early on, but perhaps it's worth
> discussing further?
>

Yeah. Side benefit, the 'action_number' felt really out of place, and
that neatly might solve it. It doesn't match tg_op, for example. With the
current approach, return a text, or an enum? Why doesn't it match concepts
that are pretty well established elsewhere? SQL has a pretty good track
record for not inventing weird numbers with no real meaning (sadly, not so
much the developers). Having said that, pg_merge_action() doesn't feel
too bad if the syntax issues can be worked out.

Very supportive of the overall goal.

merlin