mysql myisam外键

-- 创建customers表
CREATE TABLE customers (
    customer_id INT PRIMARY KEY,
    customer_name VARCHAR(255)
) ENGINE=InnoDB;

-- 创建orders表，并添加外键约束
CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    order_date DATE,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
) ENGINE=InnoDB;

-- 创建customers表（MyISAM引擎）
CREATE TABLE customers (
    customer_id INT PRIMARY KEY,
    customer_name VARCHAR(255)
) ENGINE=MyISAM;

-- 创建orders表（MyISAM引擎）
CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    order_date DATE
) ENGINE=MyISAM;

-- 插入数据时手动检查外键约束
DELIMITER $$
CREATE TRIGGER check_customer_id_before_insert
BEFORE INSERT ON orders
FOR EACH ROW
BEGIN
    DECLARE customer_exists INT;
    SELECT COUNT(*) INTO customer_exists FROM customers WHERE customer_id = NEW.customer_id;
    IF customer_exists = 0 THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Customer ID does not exist';
    END IF;
END$$
DELIMITER ;