What is a primary key in MySQL?

A primary key is a column or set of columns that uniquely identifies each row in a table and cannot contain NULL values.

Why should I use foreign keys in my database?

Foreign keys enforce referential integrity by linking tables and preventing inconsistent or orphaned data.

What does normalization achieve in database design?

Normalization reduces data duplication and dependency, improving data consistency and simplifying maintenance.

Can a table have more than one primary key?

No, a table can have only one primary key, but it can be composed of multiple columns (composite key).

MySQL Fundamentals - Basic Database Design Tutorial for Beginners

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Normalization: Reducing Data Redundancy

Normalization is a process of organizing data to minimize duplication and dependency.

It involves dividing large tables into smaller, related tables and defining relationships between them.

First Normal Form (1NF): Eliminate repeating groups; ensure atomic columns.
Second Normal Form (2NF): Remove partial dependencies on a composite key.
Third Normal Form (3NF): Remove transitive dependencies.

Normalization Forms Overview
Normalization Form	Description
1NF	Ensure each column contains atomic values; no repeating groups.
2NF	All non-key columns fully depend on the primary key.
3NF	No transitive dependencies; non-key columns depend only on the primary key.

Examples

Creating a Simple Customers Table with Primary Key

CREATE TABLE Customers (
  CustomerID INT AUTO_INCREMENT PRIMARY KEY,
  FirstName VARCHAR(50),
  LastName VARCHAR(50),
  Email VARCHAR(100)
);

This example creates a Customers table with a unique CustomerID as the primary key.

Defining a Foreign Key Relationship

CREATE TABLE Orders (
  OrderID INT AUTO_INCREMENT PRIMARY KEY,
  OrderDate DATE,
  CustomerID INT,
  FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

The Orders table references the Customers table via CustomerID, establishing a relationship.

Topic information

Learning Objectives

Introduction

Recommended Next Topics

Numeric Data Types

String Data Types

Date and Time Types

Boolean Data Types

Related Topics

Related Courses

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Understanding Tables and Columns

Primary Keys: Uniquely Identifying Records

Foreign Keys and Table Relationships

Normalization: Reducing Data Redundancy

Practical Example

Examples

Best Practices

Common Mistakes

Hands-on Exercise

Design a Simple Database Schema

Identify Normal Forms

Interview Questions

What is the purpose of a primary key in a MySQL table?

How do foreign keys help maintain data integrity?

What is database normalization and why is it important?

MCQ Quiz

Key Takeaways

Summary

Frequently Asked Questions

What is a primary key in MySQL?

Why should I use foreign keys in my database?

What does normalization achieve in database design?

Can a table have more than one primary key?

JSON Data Type

ENUM and SET

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