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:
1 2 3 4 5 6 | 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:
1 2 3 4 5 6 | 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
[youtube https://www.youtube.com/watch?v=eTK9TLciRpU]
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.