Enumeration

What is an enumeration?

An enumeration is a named set of named integer constants.

An enumeration is what?

Let's take an example:

CREATE ENUM gender_t = {
  NA = -1,
  feminine = 1,
  masculine = 2
}

This creates a named set (the name is "gender_t") of named integer constants (for example, the integer constant "1" is given the name "feminine").

OK, I get it. Any restrictions?

Yes. Both the enumeration name ("gender_t" above) and the enumeration constant names (e.g., "NA", "masculine") must be identifiers.

Also, you can't have two constants with the same value in the same enumeration. It is a set, not only in the names, but also in the values.