How to Create relationship with more than one foreign key
I guess you want do something like this:

CREATE TABLE product (category INT NOT NULL,
                      id INT NOT NULL, price DECIMAL,
                      PRIMARY KEY(category, id)
                     ) ENGINE=INNODB;

CREATE TABLE customer (id INT NOT NULL,
                       PRIMARY KEY (id)
                      ) ENGINE=INNODB;

CREATE TABLE product_order (no INT NOT NULL AUTO_INCREMENT,
                            product_category INT NOT NULL,
                            product_id INT NOT NULL,
                            customer_id INT NOT NULL,
                            PRIMARY KEY(no),
                            INDEX (product_category, product_id),
                            INDEX (customer_id),
                            FOREIGN KEY (product_category, product_id)
                                REFERENCES product(category, id)
                                ON UPDATE CASCADE ON DELETE RESTRICT,
                            FOREIGN KEY (customer_id)
                                REFERENCES customer(id)
                          ) ENGINE=INNODB;


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