What is a Primary Key and a Foreign Key?

Primary Key (PRIMARY KEY):

• A unique identifier for a record in a table.
• Does not allow duplicates or NULL values.
• Can consist of one or more columns (composite key).

MySQL 8.1
CREATE TABLE students (
    student_id INT PRIMARY KEY,
    name VARCHAR(100),
    age INT
);

Foreign Key (FOREIGN KEY)

• A column or set of columns that refer to the primary key of another table.
• Ensures referential integrity between tables.
• Allows linking records from different tables.

MySQL 8.1
CREATE TABLE enrollments (
    enrollment_id INT PRIMARY KEY,
    student_id INT,
    course_id INT,
    FOREIGN KEY (student_id) REFERENCES students(student_id),
    FOREIGN KEY (course_id) REFERENCES courses(course_id)
);