像许多事情一样，这是一种权衡。这是一个你想在哪里进行验证数据完整性的工作的问题:

(1)使用外键(单点配置为一个表，功能已经实现，经过测试，证明有效)

(2)把它留给数据库的用户(可能多个用户/应用程序更新同一个表)，这意味着更多潜在的故障点和测试的复杂性)。

数据库执行(2)更有效，使用(1)更容易维护，风险更小。

“它们会使删除记录变得更加麻烦——你不能删除“主”记录，而其他表中的记录中有外键会违反这种约束。”

重要的是要记住，SQL标准定义了删除或更新外键时所采取的操作。 我所知道的是:

ON DELETE RESTRICT - Prevents any rows in the other table that have keys in this column from being deleted. This is what Ken Ray described above. ON DELETE CASCADE - If a row in the other table is deleted, delete any rows in this table that reference it. ON DELETE SET DEFAULT - If a row in the other table is deleted, set any foreign keys referencing it to the column's default. ON DELETE SET NULL - If a row in the other table is deleted, set any foreign keys referencing it in this table to null. ON DELETE NO ACTION - This foreign key only marks that it is a foreign key; namely for use in OR mappers.

这些相同的操作也适用于ON UPDATE。

默认值似乎取决于您使用的sql server。

跨应用程序生命周期的可维护性和稳定性如何?大多数数据的生命周期都比使用它的应用程序长。关系和数据完整性非常重要，不能寄希望于下一个开发团队在应用程序代码中做出正确的处理。如果您没有使用过不尊重自然关系的脏数据的db，那么您将会使用。数据完整性的重要性将变得非常清楚。

我不得不在这里第二多的评论，外键是必要的项目，以确保你有完整的数据。ON DELETE和ON UPDATE的不同选项将允许你绕过一些人们在这里提到的关于它们的使用的“下降”。

我发现在我99%的项目中，我会使用FK来加强数据的完整性，然而，在很少的情况下，我的客户必须保留他们的旧数据，不管它有多糟糕....但后来我花了很多时间写代码，只得到有效的数据，所以它变得毫无意义。

我一直认为不用它们是懒惰的表现。我被教导应该一直这样做。但后来，我没有听乔尔的讨论。他也许有充分的理由，我不知道。

From my experience its always better to avoid using FKs in Database Critical Applications. I would not disagree with guys here who say FKs is a good practice but its not practical where the database is huge and has huge CRUD operations/sec. I can share without naming ... one of the biggest investment bank of doesn't have a single FK in databases. These constrains are handled by programmers while creating applications involving DB. The basic reason is when ever a new CRUD is done it has to effect multiple tables and verify for each inserts/updates, though this won't be a big issue for queries affecting single rows but it does create a huge latency when you deal with batch processing which any big bank has to do as daily tasks.

最好避免fk，但它的风险必须由程序员来处理。