Error SQL query: Copy ALTER TABLE `categories` ADD CONSTRAINT `parent category` FOREIGN KEY (`parent_id`) REFERENCES `parents`(`id`) ON DELETE RESTRICT ON UPDATE RESTRICT; MySQL said: Documentation #1215 - Cannot add foreign key constraint code example

CREATE TABLE Orders (
    OrderID int NOT NULL,
    OrderNumber int NOT NULL,
    PersonID int,
    PRIMARY KEY (OrderID),
    FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);