On Thu, Jun 30, 2022 at 1:43 PM Robert Haas <robertmh...@gmail.com> wrote: > rhaas=# insert into foo values (1, 'frob') on conflict (a) do update > set b = (select b || 'nitz' from excluded); > ERROR: relation "excluded" does not exist > LINE 1: ...ct (a) do update set b = (select b || 'nitz' from excluded); > > I do find that a bit of a curious error message, because that relation > clearly DOES exist in the range table.
Let's say that we supported this syntax. I see some problems with that (you may have thought of these already). Thinking of "excluded" as a separate table creates some very thorny questions, such as: How would the user be expected to handle the case where there was more than a single "row" in "excluded"? How could the implementation know what the contents of the "excluded table" were ahead of time in the multi-row-insert case? We'd have to know about *all* of the conflicts for all rows proposed for insertion to do this, which seems impossible in the general case -- because some of those conflicts won't have happened yet, and cannot be predicted. The "excluded" pseudo-table is conceptually similar to an from_item alias used within an UPDATE .... FROM ... where the target table is also the from_item table (i.e. there is a self-join). There is only one table involved. -- Peter Geoghegan
