On 11/1/23 11:12, Dean Rasheed wrote:
On Tue, 31 Oct 2023 at 23:19, Vik Fearing <v...@postgresfriends.org> wrote:
On 10/31/23 19:28, Jeff Davis wrote:
Assuming we have one RETURNING clause at the end, then it creates the
problem of how to communicate which WHEN clause a tuple came from,
whether it's the old or the new version, and/or which action was
performed on that tuple.
How do we communicate any of those things? We need to get that
information into the result table somehow, so it should probably be
some kind of expression that can exist in the RETURNING clause. But
what kind of expression?
(a) It could be a totally new expression kind with a new keyword (or
recycling some existing keywords for the same effect, or something that
looks superficially like a function call but isn't) that's only valid
in the RETURNING clause of a MERGE statement. If you use it in another
expression (say the targetlist of a SELECT statement), then you'd get a
failure at parse analysis time.
This would be my choice, the same as how the standard GROUPING()
"function" for grouping sets is implemented by GroupingFunc.
Something I'm wondering about is to what extent this discussion is
driven by concerns about aspects of the implementation (specifically,
references to function OIDs in code), versus a desire for a different
user-visible syntax. To a large extent, those are orthogonal
questions.
For my part, I am most concerned about the language level. I am
sympathetic to the implementers' issues, but that is not my main focus.
So please do not take my implementation advice into account when I voice
my opinions.
--
Vik Fearing
