Re: [HELP] Attribute has an unknown type/is repeated

"Itzinger, Oskar" <oitzinger@opec.org> writes:
> 1. What exactly is the type of colx in Case 1?
> 2. Why can't PostgreSQL infer that very same type for colx in Case 2?

The || operator is known to yield a result of type "text".  But when the
sum total of the known information is

    '' AS colx

there is no basis at all for assigning a specific type, and it remains
"unknown".

            regards, tom lane