为什么外键不更新? [英] Why foreign key doesn't update?
问题描述
我将数据插入到TEMP1.aa列中(temp1中的主键)，但不会导入到TEMP2.cc列中(temp2中的外键).
I insert data in the column TEMP1.aa (primary key in temp1), but it doesn't import into the TEMP2.cc column (foreign key in TEMP2).
为什么?
我认为如果在主键中插入数据，它将自动插入到外键中！如果是这样，那么如果我们插入主键，必须更新外键吗?
I thought if insert data in primary key it automatic insert into foreign key! If this true that if we insert in a primary key, foreign key must be updated?
推荐答案
外键不会更新子引用，它只能确保存储在该列中的值已经存在于父表中.
A foreign key does not update child references, it only ensures that the value stored in the column already exists in the parent table.
但是MySQL通过在TEMP1表的外键约束中添加ON UPDATE CASCADE来支持级联更新.否则，您需要考虑使用触发器来制定更详细的规则/要求.
But MySQL supports cascading an update, by adding the ON UPDATE CASCADE to the foreign key constraint in the TEMP1 table. Otherwise, you need to consider using a trigger for more elaborate rules/requirements.
参考:
- MySQL - Foreign Key Constraints documentation
- MySQL - Triggers documentation
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