Question

For example I want to make my own Boolean type and call it Bool. How do I do that?

Or a type for traffic lights, i.e. that has only Red, Yellow, Green in it (and null of course).

Answer 1

The closest think I could think of is:

create or replace type lights as object
(
  red varchar2(8),
  yellow varchar2(8),
  green varchar2(8),
constructor function lights return self as result
)

and the body:

create or replace type body lights is
constructor function lights return self as result is
begin
  self.red = 'red';
  self.yellow = 'yellow';
  self.green = 'green';
  return;
end;
end;

Then in the code you can use it:

declare
l lights := new lights;
begin
   dbms_output.put_line(l.red);
end;