如何使用alter table创建两个主键
我有具有此表单的表代理
broker
{
broker_code char(10) primary key
.
.
.
}
添加了另一个主键
，并且我已使用此表单代码 int nut null auto_increment
，并编写了此查询
ALTER TABLE broker ADD code INT NOT NULL AUTO_INCREMENT,
ADD PRIMARY KEY (code);
，但出现此错误。
multiply primary key defined.
我能做些什么？
I have table broker with this form
broker
{
broker_code char(10) primary key
.
.
.
}
and i have add to it another primary key with this form
code int nut null auto_increment
and wrote this query
ALTER TABLE broker ADD code INT NOT NULL AUTO_INCREMENT,
ADD PRIMARY KEY (code);
but it this error.
multiply primary key defined.
what can i do?
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您不能有两个主键...但是，您可以有一个“候选”键或唯一键，它也可以防止在其他条件上重复...例如人力资源应用程序中的人员。您可以有一个内部“员工 ID”，它是主要的，但也是一个人的社会安全号码的候选密钥，该号码永远不应该重复......如果是这样，它将向 H/R 发出危险信号验证一个人是谁。
You can't have two primary keys... However, you can have a "candidate" key or Unique that also prevents duplication on other criteria... Such as a person in a human resources application. You can have an internal "employee ID" which is the primary, but also a candidate key on a person's Social Security Number which SHOULD never be duplicated... and if so, it would through up a red-flag to H/R to verify who a person is.
下面的代码有一个带有更改表的复合主键。
This code below has a composite primary key with alter table.
我不确定，因为我看不到您当前表“经纪人”的结构。
但我的猜测是您已经定义了另一个主键。
每个表只能有 1 个主键。
I'm not sure because I can't see the structure of your current table 'broker'.
But my guess is that you already defined another Primary Key.
You are only allowed to have 1 primary key per table.