一个表中可以有多个主键吗?

问题描述：

一个表中可以有多个主键吗?

Can I have multiple primary keys in a single table?

答

一个表可以有一个复合主键，它是由两列或更多列组成的主键.例如:

A Table can have a Composite Primary Key which is a primary key made from two or more columns. For example:

CREATE TABLE userdata (
  userid INT,
  userdataid INT,
  info char(200),
  primary key (userid, userdataid)
);

更新: 这里是链接与复合主键的更详细说明.

Update: Here is a link with a more detailed description of composite primary keys.