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。

您可以通过使用整数主键来提高性能。

这取决于桌子。如果表中的行表示电子邮件地址，那么电子邮件是最好的ID。如果不是，那么电子邮件不是一个好的ID。

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。

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。

似乎没有人提到一个可能的问题，即电子邮件地址可能被视为隐私。如果电子邮件地址是主键，那么个人资料页面的URL很可能类似于..../Users/my@email.com。如果不想暴露用户的电子邮件地址怎么办?您必须找到其他一些识别用户的方法，可能是通过一个唯一的整数值来生成像..../Users/1这样的url。那么你最终会得到一个唯一的整数值。