Re: BUG #16958: "Invalid reference to FROM-clause entry for table" when qualifying columns in "on conflict .. where"

Peter Geoghegan <pg(at)bowt(dot)ie> writes:
> On Sat, Apr 10, 2021 at 9:28 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> It does seem like a pointless prohibition, but the comment about it in
>> the source code implies it was intentional. Peter, do you remember
>> why?

> No. The intention was to make it like CREATE INDEX. Apparently CREATE
> INDEX allows the columns to be qualified, though, so that explanation
> doesn't justify it.

OK. Here's a more fleshed-out patch that makes an effort to get rid of
duplicate namespace-munging.

I found that creating the EXCLUDED RTE soon enough to draw the complaint
I wanted about bogus references also caused this interesting change in
the regression test results:

ERROR: column "keyy" does not exist
LINE 1: ...nsertconflicttest values (1, 'Apple') on conflict (keyy) do ...
^
-HINT: Perhaps you meant to reference the column "insertconflicttest.key".
+HINT: Perhaps you meant to reference the column "insertconflicttest.key" or the column "excluded.key".
-- Have useful HINT for EXCLUDED.* RTE within UPDATE:

This seems to me like an independent bug: why is the misspelled-column-
name hint machinery including inaccessible columns in its results?
That seems much more likely to be confusing than helpful. But if there
is actually a defensible reason for doing that, then this seems like
an okay change.

regards, tom lane