如何创建一个在SQL中只允许存在一个子类型的ISA层次结构？

CREATE TABLE Animal (
    AnimalID INT PRIMARY KEY,
    Name VARCHAR(100),
    BirthDate DATE
);

CREATE TABLE Dog (
    AnimalID INT PRIMARY KEY,
    Breed VARCHAR(100),
    FOREIGN KEY (AnimalID) REFERENCES Animal(AnimalID)
);

CREATE TABLE Cat (
    AnimalID INT PRIMARY KEY,
    Color VARCHAR(50),
    FOREIGN KEY (AnimalID) REFERENCES Animal(AnimalID)
);

-- 插入一个动物
INSERT INTO Animal (AnimalID, Name, BirthDate) VALUES (1, 'Buddy', '2020-05-15');

-- 插入一个狗
INSERT INTO Dog (AnimalID, Breed) VALUES (1, 'Golden Retriever');

CREATE TRIGGER trg_CheckSubtype
BEFORE INSERT ON Dog
FOR EACH ROW
BEGIN
    DECLARE count INT;
    SELECT COUNT(*) INTO count FROM Cat WHERE AnimalID = NEW.AnimalID;
    IF count > 0 THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'This AnimalID already exists in Cat table';
    END IF;
END;