MYSQL - 什么是主键? [英] MYSQL - What is a primary key?

问题描述

我正在学习Mysql，我正在创建数据库.所以，看了几个网站后，主键的定义是:

I'm in the process of learning Mysql, and I'm creating databases. So, after looking at several websites, the definition for a primary key is:

PRIMARY KEY 约束唯一标识数据库表中的每条记录.

The PRIMARY KEY constraint uniquely identifies each record in a database table.

并像这样使用:

    CREATE TABLE Persons
(
    P_Id int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Address varchar(255),
    City varchar(255),
    PRIMARY KEY (P_Id)          //primary key is on this line
)

然而，我仍然不知道它的用途以及我们为什么需要它.所以我的问题是.

However, I still don't know what it's used for and why we need it. So my question is.

有人可以向我解释什么是主键(基本英语)以及我们为什么需要一个主键以及它的用途是什么?

Can someone explain to me what a primary key is (in basic english) and why we need one and what is it used for?

谢谢.

推荐答案

A 主键是一个列，它被定义为唯一标识表格中的每一行.

A primary key is a column that is defined as uniquely identifying each row in a table.

此外，通过将列定义为 PRIMARY KEY，它可以被引用为 外键 定义参照完整性a> 约束.

Also, by defining a column as PRIMARY KEY, it may be referenced as a foreign key in other tables when defining referential integrity constraints.

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