数据库MN关系 [英] Database MN relationship

问题描述

我在数据库管理系统（绝对初学者）上课，我正在一个非常简单的博客系统的数据库。

我有一个关于博客帖子和帖子所属类别之间的一个M：N关系的问题（一个博客帖子可以分成几个类别。）

计划的部分如下所示：
计划

我知道这种方案允许添加不属于任何类别的博客帖子。但是，我不知道为什么。

解决方案

这可能是两件事的组合。一个是你的数据库设计中缺乏引用完整性，即你需要外键。另一个是你的前端应用程序允许博客没有类别的发布。

I'm taking a class on database management systems (absolute beginner) and I'm working on a database for a very simple blog system.

I have a question regarding one M:N relationship between blog posts and categories where the posts belong (one blog posts can be in several categories.)

The part of the scheme looks like this: Scheme

I know that somehow this scheme allows to add a blog post that doesn't belong to any category. However, I don't know why that is. Could someone please explain this to me?

Thanks.

解决方案

It's probably a combination of two things. One would be a lack of referential integrity in your database design, ie you need foreign keys. The other would be that your front end application is allowing blogs without categories to be posted.

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