What is the automatic connection mechanism of foreign keys and primary keys in MySQL?-Mysql Tutorial-php.cn

What is the automatic connection mechanism of foreign keys and primary keys in MySQL?

The automatic connection mechanism between foreign keys and primary keys in MySQL is achieved by establishing foreign key constraints. A foreign key constraint is a relational constraint that associates a field in one table with a field in another table to ensure data consistency and integrity. The primary key is a field in a table that uniquely identifies each row of data, while the foreign key is the primary key in another table and is used to establish an association between tables.

In MySQL, when we define a foreign key in a table and specify its corresponding primary key, MySQL will automatically establish a connection between the tables. The following is a specific code example to demonstrate the automatic connection mechanism of foreign keys and primary keys in MySQL:

First we create a main tableusersand set its primary key touser_id：

CREATE TABLE users ( user_id INT PRIMARY KEY, username VARCHAR(50) );

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Next, we create a slave tableorders, by defining the foreign keyuser_idin theorderstable, and the main table ## Primary keyuser_idof #usersCreate association:

CREATE TABLE orders ( order_id INT PRIMARY KEY, order_date DATE, user_id INT, FOREIGN KEY (user_id) REFERENCES users(user_id) );

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In the above code, the

user_idfield in theorderstable is the same as theuser_idin theuserstable The fields establish foreign key constraints, thus realizing the automatic connection mechanism between theorderstable and theuserstable. When we insert data into theorderstable, if the inserteduser_iddoes not exist in theuserstable, the check of the foreign key constraint will be triggered to ensure that the data of integrity.

In short, the automatic connection mechanism of foreign keys and primary keys in MySQL realizes the association between tables through foreign key constraints to ensure the consistency and integrity of the data.

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