数据库中的一对一关系和一对多关系之间的差异 [英] Difference between one-to-one and one-to-many relationship in database

问题描述

这可能是一个基本的（愚蠢的）问题，但是当在数据库中具有一对一的关系时，另一个表有一个外键ID（在这个例子中）。在一对多关系中，表包含许多外键。

This is probably a basic(dumb) question but when having a one-to-one relationship in a database the other table has a foreign key ID(in this example). And in a one-to-many relationship the table contains many foreign keys.

但是数据库不知道这是一对一还是一对多的关系呢？我在ER-Diagram中所做的关系只是表示在制作实际表格时应该是外键的位置？

But the database does not know whether this is a one-to-one or one-to-many relationship right? The relationships that I make in an ER-Diagram is only to indicate where it should be foreign keys when making the actual tables?

我不完全理解

提前感谢。

推荐答案

在某种意义上，我们谈论的所有关系都不是已知的数据库，它们是我们发明的结构，以更好地了解如何设计表。

In a sense, all the relationships we talk about are not known to the database, they are constructs we have invented to better understand how to design the tables.

在一对一和一对多之间的表结构方面的巨大区别在于，在一对一中，有可能（但不必要）具有双向关系，意思表A可以有一个外键进入表B，并且表B可以有一个外键进入表A中的相关记录。这是一个一对多关系不可能的。

The big difference in terms of table structure between one-to-one and one-to-many is that in one-to-one it is possible (but not necessary) to have a bidirectional relationship, meaning table A can have a foreign key into table B, and table B can have a foreign key into the associated record in table A. This is not possible with a one-to-many relationship.

一对一关系将一个表中的一个记录与另一个表中的单个记录相关联。一对多关系将一个表中的一个记录与另一个表中的许多记录相关联。

One-to-one relationships associate one record in one table with a single record in the other table. One-to-many relationships associate one record in one table with many records in the other table.

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