The method of adding Foreign Keys in mysql

Editor to share with you how to add foreign keys to mysql, I believe that most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Mysql how to add foreign keys, adding foreign keys shows that there is not only one table, but also there is an association between tables.

First, add a foreign key when you create the table.

1: create a parent table with the primary key as the foreign key of the child table:

Create table province (pId int primary key auto_increment, pName varchar (20)

2: create a child table, and the foreign key is the primary key of the parent table:

Create table user (userId int primary key auto_increment, userName varchar (40), pid int, foreign key (pid) references province (pId))

Add a foreign key to a table, that is, the rule of adding a primary key to the foreign key of a child table:

Declare a field pid int in the child table as the foreign key of the child table, foreign key (the foreign key field of the child table) the table name of the references parent table (the field name of the primary key of the parent table)

Add foreign key constraints when you create the datasheet:

After creating the child table, create a foreign key

Create table user (userId int primary key auto_increment, userName varchar (40), pid int); alter table user add foreign key (pid) references province (pId)

Data table name of the alter table child table add foreign key (foreign key name of the child table) references the data table name of the parent table (the primary key name of the parent table)

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