本文介绍了如何在ALTER TABLE语句中添加"ON DELETE CASCADE"的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我的表中有一个外键约束，我想向其添加ON DELETE CASCADE.
I have a foreign key constraint in my table, I want to add ON DELETE CASCADE to it.
我已经尝试过了:
alter table child_table_name
modify constraint fk_name
foreign key (child_column_name)
references parent_table_name (parent_column_name) on delete cascade;
不起作用.
外键已经存在，外键列中有数据.
Foreign key already exists, there are data in foreign key column.
执行该语句后收到的错误消息:
The error message I get after executing the statement:
ORA-02275: such a referential constraint already exists in the table
推荐答案
您不能将ON DELETE CASCADE添加到已经存在的约束中.您将必须drop并重新create约束. 文档显示MODIFY CONSTRAINT子句只能修改约束状态(即:ENABLED/DISABLED ...).
You can not add ON DELETE CASCADE to an already existing constraint. You will have to drop and re-create the constraint. The documentation shows that the MODIFY CONSTRAINT clause can only modify the state of a constraint (i-e: ENABLED/DISABLED...).
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