Re: MERGE ... RETURNING

On Fri, 2024-03-15 at 11:20 +0000, Dean Rasheed wrote:
> To recap, this adds support for a single RETURNING list at the end of
> a MERGE command, and a special MERGE_ACTION() function that may be
> used in the RETURNING list to return the action command string
> ('INSERT', 'UPDATE', or 'DELETE') that was executed.

...

> So barring any further objections, I'd like to go ahead and get this
> patch committed.

All of my concerns have been extensively discussed and it seems like
they are just the cost of having a good feature. Thank you for going
through so many alternative approaches, I think the one you've arrived
at is consistent with what Vik endorsed[1].

The MERGE_ACTION keyword is added to the 'col_name_keyword' and the
'bare_label_keyword' lists. That has some annoying effects, like:

   CREATE FUNCTION merge_action() RETURNS TEXT
      LANGUAGE SQL AS $$ SELECT 'asdf'; $$;
   ERROR:  syntax error at or near "("
   LINE 1: CREATE FUNCTION merge_action() RETURNS TEXT

I didn't see any affirmative endorsement of exactly how the keyword is
implemented, but that patch has been around for a while, and I didn't
see any objection, either.

I like this feature from a user perspective. So +1 from me.

Regards,
    Jeff Davis

[1]
https://www.postgresql.org/message-id/7db39b45-821f-4894-ada9-c19570b11b63@postgresfriends.org