"David G. Johnston" <david.g.johnston@gmail.com> writes:
> This seems to fail to answer the OPs question. Specifically, do these
> rules automatically, or at least if #1 is not true, cause typemod
> information to be lost? IOW, is it because of the unknown that both end up
> up-casted to typemod-less text?
Any mismatch of typmod will result in the merged column being considered
to have no typmod. There is no provision for identifying a "common
superset" typmod. It would have to be some type-specific API, since the
encoding of typmod is type-specific; and we don't have one.
regards, tom lane
