Enforcing Standards With SubType

Create a new type by adding restrictions to an existing type with 'SubType.'

Create Or Replace Package p_Std
is
    SubType City  is VARCHAR2(25)   ;
    SubType State is CHAR(2)         not null ;
end;
/

These can now be referenced:

Declare
    v_City   p_Std.City  := 'Pittsburgh';
    v_St     p_Std.State := 'PA'        ;
Begin
    Dbms_Output.Put_Line (v_City ||', '||v_St);
End;
/
Pittsburgh, PA

PL/SQL procedure successfully completed.