Re: [HACKERS] MERGE SQL Statement for PG11

Take for example the "sub-selects are not supported" limitation. It's
not clear to me why this does not work. I see claims that SQL standard
says something about it (but not what exactly), that it supposedly
depends on how we handle concurrency, and perhaps other reasons.
Furthermore, there are multiple places where the sub-select might be,
and I'm not sure which of those arguments applies to which case.

Without answering (2) I think it's perfectly understandable Peter is
concerned we may run into design issues later, when we try to address
some of the limitations.


I plan to go through the patch and this thread over the couple of days,
and summarize what the current status is (or my understanding of it).
That is (a) what are the missing pieces, (b) why are they missing, (c)
how we plan to address them in the future and (d) opinions on these
issues expressed by others on this thread.