Re: MERGE ... RETURNING

Dean Rasheed <dean.a.rasheed@gmail.com>

From: Dean Rasheed <dean.a.rasheed@gmail.com>

To: Vik Fearing <vik@postgresfriends.org>

Cc: Isaac Morland <isaac.morland@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2023-01-09T17:44:36Z

Lists: pgsql-hackers

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Add RETURNING support to MERGE.
- c649fa24a42b 17.0 landed
doc: Improve a couple of places in the MERGE docs.
- 97d4262683ac 17.0 landed
- d4c573d8e81e 16.3 landed
- a875743ff402 15.7 landed
doc: improve description of privileges for MERGE and update glossary.
- 4bc8f29088f8 17.0 landed
- 3b6728910ace 16.2 landed
- ff772853d02e 15.6 landed
Fix RLS policy usage in MERGE.
- c2e08b04c9e7 17.0 cited
Fix leak of LLVM "fatal-on-oom" section counter.
- 4f4d73466d71 17.0 cited
Implement outer-level aggregates to conform to the SQL spec, with
- e649796f128b 7.4.1 cited

On Mon, 9 Jan 2023 at 16:23, Vik Fearing <vik@postgresfriends.org> wrote:
>
> Bikeshedding here.  Instead of Yet Another WITH Clause, could we perhaps
> make a MERGING() function analogous to the GROUPING() function that goes
> with grouping sets?
>
> MERGE ...
> RETURNING *, MERGING('clause'), MERGING('action');
>

Hmm, possibly, but I think that would complicate the implementation quite a bit.

GROUPING() is not really a function (in the sense that there is no
pg_proc entry for it, you can't do "\df grouping", and it isn't
executed with its arguments like a normal function). Rather, it
requires special-case handling in the parser, through to the executor,
and I think MERGING() would be similar.

Also, it masks any user function with the same name, and would
probably require MERGING to be some level of reserved keyword.

I'm not sure that's worth it, just to have a more standard-looking
RETURNING list, without a WITH clause.

Regards,
Dean