Re: MERGE ... RETURNING

On Mon, 13 Mar 2023 at 13:36, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>
> And another rebase.
>

I ran out of cycles to pursue the MERGE patches in v16, but hopefully
I can make more progress in v17.

Looking at this one with fresh eyes, it looks mostly in good shape. To
recap, this adds support for the RETURNING clause in MERGE, together
with new support functions pg_merge_action() and
pg_merge_when_clause() that can be used in the RETURNING list of MERGE
to retrieve the kind of action (INSERT/UPDATE/DELETE), and the index
of the WHEN clause executed for each row merged. In addition,
RETURNING support allows MERGE to be used as the source query in COPY
TO and WITH queries.

One minor annoyance is that, due to the way that pg_merge_action() and
pg_merge_when_clause() require access to the MergeActionState, they
only work if they appear directly in the RETURNING list. They can't,
for example, appear in a subquery in the RETURNING list, and I don't
see an easy way round that limitation.

Attached is an updated patch with some cosmetic updates, plus updated
ruleutils support.

Regards,
Dean