Re: [HACKERS] MERGE SQL Statement for PG11

Apparently there is a pending patch to do better there - the commit
message of 2f178441 refers to this.

> The revised version also supports subqueries in SET targetlist as well as
> WHEN AND conditions. As expected, this needed a minor tweak in
> query/expression mutators. So once I worked on that for partitioned tables,
> subqueries started working with very minimal adjustments elsewhere. Other
> things such as whole-var references are still broken. A few new tests are
> also added.

Great!

Wholerow references are expected to be a bit trickier. See commit
ad227837 for some hints on how you could fix this.

> Next I am going to look at RLS. While I've no prior experience with RLS, I
> am expecting it to be less cumbersome in comparison to partitioning. I am
> out of action till Monday and may not be able to respond in time. But any
> reviews and comments are appreciated as always.

I don't think that RLS support will be particularly challenging. It
might take a while.

If your rapid progress here is any indication, most open items are not
likely to be particularly challenging. Once again, I suggest that a
good area for us to focus on is the semantics of READ COMMITTED
conflict handling.

Maybe you'd prefer to just blast through the
simpler open items, which is fine, but do bear in mind that the EPQ
and EPQ-adjacent stuff is probably going to be the thing that makes or
breaks this patch for v11.