-- exemplo retirado do livro de texto 
-- "A First Course in Database Systems"
-- Ullman & Widom

CREATE TABLE Product
(
   maker varchar,
   model int,
   type varchar,
   PRIMARY KEY( model )
);

CREATE TABLE PC
(
   model int,
   speed int,
   ram int,
   hd numeric(5,2), 
   cd varchar,
   price int,
   PRIMARY KEY( model ),
   FOREIGN KEY( model ) REFERENCES Product
);

CREATE TABLE Laptop
(
   model int,
   speed int,
   ram int,
   hd numeric(5,2),
   screen numeric(5,2),
   price int,
   PRIMARY KEY( model ),
   FOREIGN KEY( model ) REFERENCES Product
);

CREATE TABLE Printer
(
   model int,
   color boolean,
   type varchar,
   price int,
   PRIMARY KEY( model ),
   FOREIGN KEY( model ) REFERENCES Product
);