What is a Mysql foreign key? What are the uses? (Pictures + Videos)

This article mainly introduces to you What is mysql foreign key and The role of foreign key in mysql database.

First of all, we need to briefly understand what mysql?

MySQL is a relational database management system and one of the most popular relational database management systems. In terms of WEB applications, MySQL is the best RDBMS (Relational Database Management System) application. software.

The definitions of "key" and index in MySQL are the same, so foreign keys and primary keys are also a type of index.

And the concept of mysql foreign key may not be particularly easy to understand for novices.

Let’s give a simple example to introduceWhat is mysql foreign key?

Foreign key is relative to the primary key and is a necessary prerequisite for establishing a relationship between tables.

For example, there are two tables here, the user (user) table and the qx (permission) table. The gid in user is the user permission id, and the gid depends on the id in qx. Then the id in qx is the foreign key of user.

That is, when we create a foreign key for gid, and this foreign key is the id in qx, the gid must be consistent with the id in qx. We can associate the two tables through the foreign key.

Note: MySQL will automatically index the primary keys of all tables, but foreign key fields must be explicitly indexed by the user

So what is the role of creating foreign keys?

Can associate two tables to ensure data consistency and implement some cascading operations.

The main purpose of maintaining data consistency and integrity is to control the data stored in foreign key tables. To associate two tables, foreign keys can only reference the values ​​of columns in the table! You can associate two tables to ensure data consistency and implement some cascading operations.

A brief summary of the function:

1. Don’t make the data recorded in one table too redundant.

2. Maintain data consistency and integrity.

This article is about What is mysql foreign key and The role of foreign key in mysql database. It is also very easy to understand. I hope it will be helpful to friends who need it. help!

If you want to know more about mysql, you can follow the PHP Chinese website mysql video tutorial, everyone is welcome to refer to and learn!

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