如果我从MySQL父表中删除一行会发生什么？

在从父表中删除行时，如果该行的数据在子表中使用，则MySQL将因FOREIGN KEY约束失败而抛出错误。可以用名为“customer”和“orders”的两个表的示例来理解这一点。“customer”是父表，“orders”是子表。我们无法从“customer”表中删除在子表“orders”中使用的行。可以通过从父表中删除值来演示如下：

mysql> Select * from Customer;
+----+--------+
| id | name   |
+----+--------+
| 1  | Gaurav |
| 2  | Raman  |
| 3  | Harshit|
| 4  | Aarav  |
+----+--------+
4 rows in set (0.00 sec)

mysql> Select * from orders;
+----------+----------+------+
| order_id | product  | id   |
+----------+----------+------+
| 100      | Notebook | 1    |
| 110      | Pen      | 1    |
| 120      | Book     | 2    |
| 130      | Charts   | 2    |
+----------+----------+------+
4 rows in set (0.00 sec)

现在，假设我们尝试从父表“customer”中删除id = 1或id = 2的行（因为两行都在子表中使用），那么MySQL将由于foreign key约束失败而抛出以下错误。

mysql> Delete from customer where id = 1;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`query`.`orders`, CONSTRAINT `orders_ibfk_1` FOREIGN KEY (`id`)REFERENCES `customer` (`id`))

mysql> Delete from customer where id = 2;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`query`.`orders`, CONSTRAINT `orders_ibfk_1` FOREIGN KEY (`id`)REFERENCES `customer` (`id`))

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