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在多对一表中使用哪个外键

[英]Which foreign key to use in a many-to-one table

原文 2010-09-15 00:03:56 1 3 sql/ mysql/ database/ foreign-keys

Suppose I have a table Books with columns Book_ID (Primary Key), ISBN (Unique), and several others such as Title/author/etc. 假设我有一个表包含Book_ID（主键），ISBN（唯一）和其他几个如Title / author / etc的书籍。

I have another table Sales, with primary key Sale_ID, a foreign key to link to Books, and other fields with info on Sales. 我有另一个表Sales，主键为Sales_ID，链接到Books的外键，以及包含Sales信息的其他字段。 Sales only exist for books with ISBNs. 只有具有ISBN的图书才有销售。 Is it better database design to have Book_ID or ISBN be the primary key. 将Book_ID或ISBN作为主键是更好的数据库设计吗？ Note: I will be LEFT JOINing Sales to Books on whichever the foreign key is chosen. 注意：无论选择哪个外键，我都将LEFT JOINING Sales to Books。

UPDATE: Some Books have no ISBN's because they're not published with them. 更新：有些书没有ISBN，因为它们没有与它们一起发布。 However, I don't foresee (at least in the next several years) users being able to sell them, because I have no system for making sure that a given book w/o the ISBN isn't repeated. 但是，我没有预见到（至少在接下来的几年内）用户能够出售它们，因为我没有系统来确保不会重复没有ISBN的给定书籍。

3 个解决方案

我会一直使用你的主键

In general, I think I would go for the surrogate primary key book_id as the foreign key. 一般来说，我认为我会将代理主键 book_id作为外键。

There are a few potential issues that I can identify if you were to use the non-primary key ISBN as a foreign key: 如果您要将非主键ISBN用作外键，我可以识别一些潜在问题：

You might have a missing or unknown ISBN for a particular book. 对于特定图书，您可能缺少或未知ISBN 。 What would you do in case there is a sale of that book? 如果出售那本书，你会怎么做？
You might have an incorrect ISBN . 您的ISBN可能不正确。 To edit it, you would have to update all the tables that would be using it as a foreign key. 要编辑它，您必须更新将其用作外键的所有表。
You might want to start selling books that don't have an ISBN in the future. 您可能希望以后开始销售没有ISBN书籍。 Why are you storing books without an ISBN in the first place? 你为什么要首先存储没有ISBN书籍？
An index on book_id should be much more compact than one on an ISBN field. book_id上的索引应该比ISBN字段上的索引更紧凑。

I would always use ISBN . 我会一直使用ISBN 。 This way you have a simple way of enforcing your business rule, "Sales only exist for books with ISBNs" ie by making the ISBN column NOT NULL in the Sales table and referencing the ISBN column in the Books table. 通过这种方式，您可以通过一种简单的方式来强制执行业务规则，“仅对具有ISBN的书籍进行销售”，即在“ Sales表格中将ISBN列NOT NULL并引用Books表格中的ISBN列。

I don't agree with @Daniel Vassallo that because you might want to start selling books that don't have an ISBN in the future you would want to drop the rule in the database today. 我不同意@Daniel Vassallo，因为你可能想要开始销售未来没有ISBN的书籍，你今天就想把这条规则放到数据库中。 There is a name for this design flaw: future creep. 这个设计缺陷有一个名称：未来的蠕变。 Also, the considerations of 'compact indexes' should always be secondary to those of basic data integrity. 此外，“紧凑索引”的考虑因素应该始终是基本数据完整性的考虑因素。