MODULE 05 · DATABASE & SQL

Normalization

Normalization organizes relational data so each fact has a clear home and unnecessary duplication is reduced.

01 · What is it?

Normalization organizes relational data to reduce unnecessary duplication and improve consistency.

It gives each fact a clear home and uses relationships to connect related facts without copying the same information everywhere.

Think of normalization like sorting a kitchen into labeled cupboards instead of keeping every ingredient in every room.

Repeated Facts

Related Tables

Consistent Updates

Reduce Duplication

Store one fact in one appropriate place.

Clarify Relationships

Connect tables with keys instead of copying whole records.

Protect Updates

Change a fact once and avoid conflicting copies.

Normalization is common in transactional systems such as accounts, orders, inventory, billing, and permissions.

A normalized order system stores customer details in a customers table, order details in orders, and the relationship through a customer key.

customers(id, name, email)
orders(id, customer_id)
order_items(order_id, product_id, quantity)

The customer email is stored once, while each order points back to the customer record.

Business Facts

Tables

Keys

SQL

Normalization

How data is organized to reduce duplication.

Indexing

How a database finds data more efficiently.

Denormalization

A deliberate choice to duplicate data for a performance or reporting need.

ENGLISH TERM	中文	SIMPLE ENGLISH	中文小白理解
Normalization	规范化	Organizing relational data to reduce unnecessary duplication.	整理关系型数据，减少不必要的重复。
Relationship	关系	A connection between related records.	相关数据记录之间的连接。
Primary Key	主键	A value that uniquely identifies a record.	唯一识别一条记录的值。
Foreign Key	外键	A value that points to a record in another table.	指向另一张表中记录的值。

Normalization gives each fact a clear home and uses relationships to connect the data.