Bruce Momjian <bruce@momjian.us> writes:
> Tom Lane wrote:
>> The approach I originally suggested was to create the enum type with
>> *no* members, and then add the values one at a time.
> Well, I was hesitant to modify the grammar, unless we want the ability
> to create enums with zero values. Doing enum with only one value will
> not be too complex for me and I don't think binary upgrade should affect
> the grammar unless there are other reasons we want to change.
The reason I don't want to do it that way is that then you need two
ugly kluges in the backend, not just one. With the zero-and-add-one
approach there is no need to have a "next enum oid" variable at all.
> We do allow tables with no columns, but we allow the addition of columns
> to a table, so it makes more sense there.
Well, we might eventually allow addition of values to enums too; the
fact that it's not implemented outside pg_migrator right now doesn't
mean we won't ever think of a solution. In any case I'm not persuaded
that a zero-element enum is totally without value. Think of it like a
domain with a "must be null" constraint.
regards, tom lane