CREATE TABLE price (
    start_price decimal(4,2) NOT NULL,
    price_date timestamp,
    PRIMARY KEY (start_price, price_date)
);

CREATE TABLE pricechange (
    start_price decimal(4,2) NOT NULL,
    new_price decimal(4,2) NOT NULL,
    price_date date NOT NULL,
    reason varchar(100),
    FOREIGN KEY (start_price, price_date)
    REFERENCES price(start_price, price_date)
);