Part A
------

CREATE TABLE suppliers (
id INT,
name CHAR(40) NOT NULL,
address CHAR(100) NOT NULL,

PRIMARY KEY (int),
UNIQUE (name,address),
CHECK (id >= 0 AND id <= 999999999)
);

CREATE TABLE products (
part_number INT,
name CHAR(100) NOT NULL,

PRIMARY KEY (part_number),
UNIQUE (name),
CHECK (id >= 1 AND id <= 999999)
);

CREATE TABLE customers (
id INT,
name CHAR(40) NOT NULL,
address CHAR(100) NOT NULL,

PRIMARY KEY (int),
UNIQUE (name,address),
CHECK (id >= 0 AND id <= 999999999)
);

CREATE TABLE contracts (
id INT,
supplier_id INT NOT NULL,
customer_id INT NOT NULL,
product_id INT NOT NULL,
quantity INT NOT NULL,
price INT NOT NULL,

PRIMARY_KEY (id),
FOREIGN KEY (supplier_id) REFERENCES suppliers(id),
FOREIGN KEY (customer_id) REFERENCES customers(id),
FOREIGN KEY (product_id) REFERENCES products(id),
CHECK (quantity > 0),
CHECK (price > 0)
);


PART B
------
CREATE ASSERTION min_contracts
  CHECK (COUNT(SELECT * FROM CONTRACTS) > COUNT(SELECT * FROM SUPPLIERS));