What is a primary key?

A primary key is a crucial concept in relational databases, serving as a unique identifier for each record within a table.

What is a Primary Key?

In a relational database, a primary key is a column or a set of columns that uniquely identifies each row (or record) in a table. It ensures that every record in the table can be distinctly identified and accessed, preventing data duplication and aiding in data integrity.

• Uniqueness: Each value in the primary key column(s) must be unique across all rows.
• Non-Nullability: A primary key column cannot contain NULL values; it must always have a value.
• Stability: Primary key values should ideally not change over time.
• Single Primary Key: A table can have only one primary key, though it can be composed of multiple columns (a composite primary key).

Why are Primary Keys Important?

Primary keys are fundamental for maintaining data integrity and enabling efficient database operations. They facilitate quick data retrieval, establish relationships between tables (through foreign keys), and enforce the uniqueness of records, thereby ensuring the consistency and reliability of the data stored in the database.

Example of a Primary Key

Consider a table named 'Students'. A common practice is to assign a unique 'student_id' to each student, which can serve as the primary key.

CREATE TABLE Students (
    student_id INT PRIMARY KEY,
    first_name VARCHAR(50),
    last_name VARCHAR(50),
    email VARCHAR(100) UNIQUE
);