create table characters_of_force ( 
  name varchar2(128) not null primary key, 
  alignment varchar2(10) not null, 
  constraint characters_of_force_chk 
    check (alignment in ('dark','light','neutral')) 
)

insert into characters_of_force 
  values ('Darth Vader', 'dark')

insert into characters_of_force 
  values ('Luke Skywalker', 'light')

insert into characters_of_force 
  values ('Aurra Sing', 'neutral')

select * from characters_of_force

create or replace package alignment_types as 
  /* the constant keyword prevents the package variable 
     from being overridden at a later time */ 
  dark constant varchar2(10) := 'dark'; 
  light constant varchar2(10) := 'light'; 
  neutral constant varchar2(10) := 'neutral'; 
end; 

begin 
  dbms_output.put_line( 
    'Anakin was first aligned to ' 
    || alignment_types.light 
    || ' but turned to ' 
    || alignment_types.dark 
    || ' later'); 
end; 

select alignment_types.light from dual

create or replace package alignment_types as 
  /* No public constants anymore, 
     but functions without parameters */ 
  function light return varchar2; 
  function dark return varchar2; 
  function neutral return varchar2; 
end; 

create or replace package body alignment_types as 
  /* Here we have our constants again, 
     hiding them from public access */ 
  g_dark constant varchar2(10) := 'dark'; 
  g_light constant varchar2(10) := 'light'; 
  g_neutral constant varchar2(10) := 'neutral'; 
 
  /* The functions are our only publicly available item */ 
  function light return varchar2 
  as 
    begin 
      return g_light; 
    end; 
 
  function dark return varchar2 
  as 
    begin 
      return g_dark; 
    end; 
 
  function neutral return varchar2 
  as 
    begin 
      return g_neutral; 
    end; 
end; 

select alignment_types.light from dual

alter table characters_of_force 
  drop constraint characters_of_force_chk

alter table characters_of_force 
  add constraint characters_of_force_chk 
  check ( alignment in 
    (alignment_types.light, 
     alignment_types.dark, 
     alignment_types.neutral) 
  )

create or replace package alignment_types as 
  function light return varchar2; 
  function dark return varchar2; 
  function neutral return varchar2; 
  /* We need a deterministic check-function */ 
  function valid_type(i_value in varchar2) 
    return int deterministic; 
end; 

create or replace package body alignment_types as 
  g_dark constant varchar2(10) := 'dark'; 
  g_light constant varchar2(10) := 'light'; 
  g_neutral constant varchar2(10) := 'neutral'; 
 
  function light return varchar2 
  as 
    begin 
      return g_light; 
    end; 
 
  function dark return varchar2 
  as 
    begin 
      return g_dark; 
    end; 
 
  function neutral return varchar2 
  as 
    begin 
      return g_neutral; 
    end; 
 
  /* This function can just check against our constants */ 
  function valid_type(i_value in varchar2) 
    return int deterministic 
  as 
    begin 
      if ( i_value in (light, dark, neutral)) then 
        return 1; 
      else 
        return 0; 
      end if; 
    end; 
end; 

alter table characters_of_force 
  add (alignment_check number generated always as ( 
    alignment_types.valid_type(alignment) 
  ))

alter table characters_of_force 
  add constraint characters_of_force_chk 
  check ( alignment_check = 1 )

insert into characters_of_force ( name, alignment ) 
  values ('Anakin Skywalker', 'confused')