如何更改外键的操作

Question

假设我有一个外键，其行为是：

on delete set default, on update cascade

如果我想更改操作，如何在alter table选项中指定它？
我试过这个：

change my_table add on delete cascade my_key;

但是它会出现语法错误：

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'on delete cascade matricola' at line 1

我想更改删除引用的主键时触发的默认操作。

Answer 1

ALTER TABLE my_table DROP FOREIGN KEY my_key;
ALTER TABLE my_table ADD CONSTRAINT my_key FOREIGN KEY ('some_id') 
        REFERENCES some_table ('id') ON UPDATE CASCADE ON DELETE CASCADE;

据我所知，您必须放弃密钥并使用新规则创建新密钥。