Primary Key Constraint

Overview

A Primary Key uniquely identifies each row in a table. It implicitly enforces both NOT NULL and UNIQUE constraints.

Learning Objectives

• Enforce entity integrity using PRIMARY KEY.
• Distinguish simple Primary Keys from Composite Primary Keys.

Code Examples

SQL

CREATE TABLE employees (
    emp_id INT PRIMARY KEY,
    name VARCHAR(100) NOT NULL
);

Summary

Primary Keys guarantee unique row identification and prevent duplicate or null key entries.