Andy Balholm <andy@balholm.com> writes:
> Is there a way to make values of "undefined" type pass through the
> SELECT DISTINCT filter (getting checked for uniqueness) but remain
> "undefined"
No. What is your criterion for deciding that two values are distinct?
It's not possible to do that without imputing a data type to them.
(In particular, comparing the character strings amounts to deciding
that they are of a textual data type --- failing to acknowledge that
isn't a workaround but merely sloppy thinking.)
regards, tom lane