Re: [HACKERS] MERGE SQL Statement for PG11

> Our regular UPDATE .. FROM does not do that
> either. Given that, it seems better to just throw an error (even when no NOT
> MATCHED action exists) and explain to the users that MERGE will work as long
> as concurrent updates don't modify the columns used in the join condition.
> Concurrent deletes should be fine and we may actually even invoke WHEN NOT
> MATCHED action in that case.

Again, I have to ask: is such an UPDATE actually meaningfully
different from a concurrent DELETE + INSERT? If so, why is a special
error better than a dup violation, or maybe even having the INSERT
(and whole MERGE statement) succeed?