This video tutorial illustrates the implementation of Primary key and Foreign key, using MySQL.
You can run the same commands / Queries shown in the video on both phpmyadmin as well as on MySQL console.
You can also look at: Primary Foreign Unique Keys, AUTO_INCREMENT: MySQL
Primary Key
The PRIMARY KEY constraint uniquely identifies each record in a database table.
Primary keys have unique values.
Primary Keys are NOT NULL by default.
Creating student table:
CREATE TABLE student(
stud_id int AUTO_INCREMENT,
name varchar(30) NOT NULL,
age int NOT NULL,
PRIMARY KEY(stud_id)
);
Foreign Key
A FOREIGN KEY in one table points to a PRIMARY KEY in another table.
Creating enrol table:
CREATE TABLE enrol(
rol_no int AUTO_INCREMENT,
stud_id int NOT NULL,
PRIMARY KEY(rol_no),
FOREIGN KEY(stud_id) REFERENCES student(stud_id)
);
Primary Key & Foreign Key Implementation: MySQL
Note:
1. You can have only 1 primary key per table. But can have zero or more foreign keys in a table.
2. You can not delete primary key row directly, without deleting all the rows referring to that row.