Error Code: 1068. Multiple primary key defined

1、错误描述

10:10:38	alter table user add num int(8) primary key first	Error Code: 1068. Multiple primary key defined	0.000 sec

2、错误原因

这个错误的原因是定义了两个主键，导致出错

3、解决办法

alter table user add num int(8) primary key first;

去掉“primary key”