mysql - 如何解决 MySQL 错误，因为错误 1215，无法添加外键约束？

Question

这是我的第一张 table 。

CREATE TABLE `raw_orders` (
`row_id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`order_id` VARCHAR(45) COLLATE utf8mb4_unicode_ci NOT NULL,
`order_revenue` FLOAT NOT NULL,
PRIMARY KEY(`row_id`),
KEY(`order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

这是我的第二张 table

CREATE TABLE `formatted_orders` (
`order_id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`client_order_id` VARCHAR(50) COLLATE utf8mb4_general_ci NOT NULL,
`order_revenue` FLOAT NOT NULL,
PRIMARY KEY(`order_id`),
KEY(`client_order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

我正在尝试使用此方法在 formatted_orders 中添加外键，将其链接到 raw_orders

ALTER TABLE formatted_orders 
ADD FOREIGN KEY (client_order_id) REFERENCES raw_orders(order_id);

但我收到此错误

ERROR (HY000): Cannot add foreign key constraint

Answer 1

您可以简单地在表 formatted_orders 中添加外键，如下所示:

CREATE TABLE `formatted_orders` (
`order_id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`client_order_id` VARCHAR(50) COLLATE utf8mb4_general_ci NOT NULL,
`order_revenue` FLOAT NOT NULL,
PRIMARY KEY(`order_id`),
FOREIGN KEY (`client_order`) REFERENCES raw_orders(`order_id`)
)