David G Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> Two approaches:
> 1. Standard virtual column name that, when used, gets rewritten into a
> constant that is stored at the table level.
> 2. A way for a column's value to be defined as a function call.
Recent versions of the SQL spec have a notion of "generated columns"
that I think subsumes both of these concepts. We had a draft patch
awhile back that attempted to implement that feature. It crashed
and burned for reasons I don't recall ... but certainly implementing
an already-standardized feature is more attractive than just inventing
behavior on our own.
regards, tom lane