MySQL复合独特的FK的 [英] MySQL composite unique on FK's

问题描述

我想在mysql中实现以下约束：

I want to implement the following constraints in mysql:

create table TypeMapping(
    ...
    constraint unique(server_id,type_id),

    constraint foreign key(server_id) references Server(id),

    constraint foreign key(type_id) references Type(id)
);

这会抛出一个错误1062（23000）：key'server_id的重复条目'3-4' ''当我发布插入/更新，将打破约束。这种类型的约束是否可能？如果是这样怎么样？谢谢。

This throws a 'ERROR 1062 (23000): Duplicate entry '3-4' for key 'server_id'' when I issue an insert/update that would break the constraint. Is this type of constraint even possible? If so how? Thank you.

推荐答案

是的，这是完全有效的。确保您理解，当您尝试在 TypeMapping 中插入新行时，复合唯一约束将会中断，其中具有相同 server_id 和 css 已经存在。

Yes, that is perfectly valid. Make sure you understand that the composite unique constraint will only break when you try to insert a new row in TypeMapping, where another row with the same server_id and type_id already exists.

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