FK 上独一无二的 MySQL 组合 [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)
);

当我发出会破坏约束的插入/更新时，这将引发错误 1062 (23000): Duplicate entry '3-4' for key 'server_id'".这种类型的约束甚至可能吗?如果有怎么办?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，这是完全正确的.确保您了解复合唯一约束只会在您尝试在 TypeMapping 中插入新行时中断，其中另一行具有相同的 server_id and type_id 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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