无法添加外键约束

-- 检查主键字段
SHOW CREATE TABLE referenced_table;

-- 检查字段数据类型
DESCRIBE referenced_table;
DESCRIBE referencing_table;

ALTER TABLE referencing_table ENGINE = InnoDB;

-- 删除或更新不符合约束的数据
DELETE FROM referencing_table WHERE foreign_key_column NOT IN (SELECT primary_key_column FROM referenced_table);

-- 查看现有外键名称
SELECT * FROM information_schema.TABLE_CONSTRAINTS WHERE CONSTRAINT_TYPE = 'FOREIGN KEY';

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

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

-- 添加外键约束
ALTER TABLE orders
ADD CONSTRAINT fk_customer
FOREIGN KEY (customer_id)
REFERENCES customers(customer_id);