On Mon, 2023-01-09 at 12:29 +0000, Dean Rasheed wrote: > > Would it be feasible to allow specifying old.column or new.column? > > These would always be NULL for INSERT and DELETE respectively but > > more useful with UPDATE. Actually I've been meaning to ask this > > question about UPDATE … RETURNING. > > > > I too have wished for the ability to do that with UPDATE ... > RETURNING, though I'm not sure how feasible it is. > > I think it's something best considered separately though. I haven't > given any thought as to how to make it work, so there might be > technical difficulties. But if it could be made to work for UPDATE, > it > shouldn't be much more effort to make it work for MERGE.
MERGE can end up combining old and new values in a way that doesn't happen with INSERT/UPDATE/DELETE. For instance, a "MERGE ... RETURNING id" would return a mix of NEW.id (for INSERT/UPDATE actions) and OLD.id (for DELETE actions). The pg_merge_action() can differentiate the old and new values, but it's a bit more awkward. I'm fine considering that as a separate patch, but it does seem worth discussing briefly here. Regards, Jeff Davis