On Thu, Oct 2, 2014 at 1:10 PM, Bruce Momjian <br...@momjian.us> wrote:
> I think if we use the MERGE command for this feature we would need to
> use a non-standard keyword to specify that we want OLTP/UPSERT
> functionality.  That would allow us to mostly use the MERGE standard
> syntax without having surprises about non-standard behavior.  I am
> thinking of how CONCURRENTLY changes the behavior of some commands.

That would leave you without a real general syntax. It'd also make
having certain aspects of an UPSERT more explicit be a harder goal
(there is no conventional join involved here - everything goes through
a unique index). Adding the magic keyword would break certain other
parts of the statement, so you'd have exact rules for what worked
where. I see no advantage, and considerable disadvantages.

Note that I've documented a lot of this stuff here:


Mapping the join thing onto which unique index you want to make the
UPSERT target is very messy. There are a lot of corner cases. It's
quite ticklish.

Please add to it if you think we've missed something.
Peter Geoghegan

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