## What is Database Normalization?
Database normalization is the process of organizing data to reduce redundancy and improve data integrity. Instead of storing the same information multiple times, you structure data efficiently so each piece of information exists in only one place.
The goal: eliminate duplicate data, prevent inconsistencies, and make your database easier to maintain.
## The Problem Without Normalization
Imagine a customer orders table that looks like this:
```
Order ID | Customer Name | Customer Email | Product
---------|---------------|---------------------|----------
1 | John Smith | john@email.com | Laptop
2 | John Smith | john@email.com | Mouse
3 | John Smith | johnsmith@email.com | Keyboard
```
Notice the problems:
- Customer info repeats on every order (wasted space)
- Email address is inconsistent (which is correct?)
- If John changes his email, you must update multiple rows
## The Solution: Normalization
Split data into separate, related tables:
**Customers Table:**
```
Customer ID | Name | Email
------------|------------|------------------
1 | John Smith | john@email.com
```
**Orders Table:**
```
Order ID | Customer ID | Product
---------|-------------|----------
1 | 1 | Laptop
2 | 1 | Mouse
3 | 1 | Keyboard
```
Now customer info exists once. Update the email in one place, and all orders reflect the change automatically.
## Normal Forms (The Levels)
Normalization happens in stages called "normal forms." Most databases aim for Third Normal Form (3NF), which covers most needs.
**First Normal Form (1NF)**: Each column contains atomic values (no lists or multiple values in one cell). Each row is unique.
**Second Normal Form (2NF)**: Meets 1NF, plus all non-key columns depend on the entire primary key.
**Third Normal Form (3NF)**: Meets 2NF, plus no column depends on another non-key column.
Higher forms exist (4NF, 5NF) but are rarely needed in practice.
## Real-World Example
An e-commerce database might have:
- **Users** table: user info
- **Products** table: product details
- **Orders** table: links users to products
- **Categories** table: product categories
- **Product_Categories** table: links products to categories
Each piece of information lives in the right place, no duplication.
## Benefits of Normalization
**No Redundancy**: Data is not repeated unnecessarily, saving storage space.
**Data Integrity**: Update information once, and it changes everywhere automatically.
**Easier Maintenance**: Clear structure makes adding features and fixing bugs simpler.
**Consistency**: Eliminates conflicting information (like two different emails for the same person).
## When NOT to Normalize
Sometimes you intentionally denormalize (add redundancy) for performance:
**Read-Heavy Applications**: Joining multiple tables is slow. Storing some duplicate data speeds up queries.
**Data Warehouses**: Analytics databases often denormalize for faster reporting.
**Caching**: Store computed values instead of calculating them repeatedly.
This is called "denormalization" and is a conscious trade-off between speed and redundancy.
## Getting Started
When designing a database:
1. Identify entities (users, products, orders)
2. Create separate tables for each entity
3. Use foreign keys to link related tables
4. Ensure each fact exists in only one place
5. Test queries to ensure data retrieves correctly
## The Balance
Perfect normalization is not always the goal. Normalize enough to eliminate problems, but denormalize when performance requires it. Experience teaches you when to break the rules.
Most applications work well with databases normalized to 3NF. Start there, and adjust based on real-world performance needs.
