我知道这有点晚了，但我想补充的是，人们放弃电子邮件帐户和服务提供商恢复地址，允许其他人使用它。

正如@HLGEM指出的那样，“Jsmith@somecompany.com很容易在一年后属于约翰·史密斯，两年后属于朱莉娅·史密斯。”在这种情况下，如果约翰·史密斯想要你的服务，你要么拒绝使用他的电子邮件地址，要么删除所有与朱莉娅·史密斯有关的记录。

如果你必须根据当地法律删除与企业财务历史有关的记录，你可能会发现自己陷入困境。

所以我永远不会使用电子邮件地址、车牌等数据作为主键，因为无论它们看起来多么独特，它们都不受你的控制，并且可能会提供一些你可能没有时间处理的有趣挑战。

使用GUID作为主键…这样，当你执行INSERT操作时，你就可以从程序中生成它，而不需要从服务器获取响应来找出主键是什么。它在所有表和数据库中都是唯一的，如果有一天你截断了表，自动增量被重置为1，你不必担心会发生什么。

使用电子邮件地址作为主键的缺点:

Slower when doing joins. Any other record with a posted foreign key now has a larger value, taking up more disk space. (Given the cost of disk space today, this is probably a trivial issue, except to the extent that the record now takes longer to read. See #1.) An email address could change, which forces all records using this as a foreign key to be updated. As email address don't change all that often, the performance problem is probably minor. The bigger problem is that you have to make sure to provide for it. If you have to write the code, this is more work and introduces the possibility of bugs. If your database engine supports "on update cascade", it's a minor issue.

使用电邮地址作主键的优点:

You may be able to completely eliminate some joins. If all you need from the "master record" is the email address, then with an abstract integer key you would have to do a join to retrieve it. If the key is the email address, then you already have it and the join is unnecessary. Whether this helps you any depends on how often this situation comes up. When you are doing ad hoc queries, it's easy for a human being to see what master record is being referenced. This can be a big help when trying to track down data problems. You almost certainly will need an index on the email address anyway, so making it the primary key eliminates one index, thus improving the performance of inserts as they now have only one index to update instead of two.

在我看来，这两种情况都不是十拿九稳的。当有实用的键时，我倾向于使用自然键，因为它们更容易使用，而且在大多数情况下，缺点并不太重要。

不要使用电子邮件地址为主键，保持电子邮件的唯一性，但不要使用它为主键，使用用户id或用户名为主键

是的，这是一个糟糕的主键，因为你的用户会想要更新他们的电子邮件地址。

就我个人而言，我在设计数据库时不使用任何信息作为主键，因为我很可能在以后需要更改任何信息。我提供主键的唯一原因是，它方便从客户端执行大多数SQL操作，我的选择一直是自动增加整数类型。