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。

您可以通过使用整数主键来提高性能。

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。

我还要指出，电子邮件是一个糟糕的选择，使一个独特的领域，有些人，甚至是小企业共享一个电子邮件地址。和电话号码一样，电子邮件也可以重复使用。Jsmith@somecompany.com很容易属于一年前的约翰·史密斯，两年后的茱莉亚·史密斯。

电子邮件的另一个问题是它们经常变化。如果你用这个键连接到其他表，那么你也必须更新其他表，当整个客户公司更改他们的电子邮件时，这可能会对性能造成相当大的影响(我曾经见过这种情况)。

我不知道这在您的设置中是否可能是一个问题，但根据您的RDBMS，列的值可能是区分大小写的。PostgreSQL文档说:“如果你声明一个列为UNIQUE或PRIMARY KEY，隐式生成的索引是区分大小写的”。换句话说，如果您在一个以email为主键的表中接受用户输入进行搜索，并且用户提供“John@Doe.com”，那么您将找不到“john@doe.com”。

您可能需要考虑任何适用的数据法规。电子邮件是个人信息，例如，如果你的用户是欧盟公民，那么根据GDPR，他们可以指示你从你的记录中删除他们的信息(记住，无论你在哪个国家，这都适用)。

如果出于参考完整性或审计等历史原因，需要将记录本身保存在数据库中，则使用代理键将允许您将所有个人数据字段设置为NULL。如果他们的个人数据是主键，这显然不那么容易