What is ERD (Entity-Relationship Diagram)?

What is an ERD?

An ERD (Entity-Relationship Diagram) shows what entities exist in a database, which attributes they have, and how they relate to each other. It makes the data model visible before or during implementation.

Core Components

• Entity: A main object represented by data, such as customer, product, or order
• Attribute: A field such as name, price, date, or status
• Relationship: A connection between two entities
• Cardinality: How many records on one side can match records on the other side
• Primary/foreign key: Record identity and references between tables

In an e-commerce system, one customer can place many orders, one order can contain many order lines, and one product can belong to a category. An ERD helps everyone understand those rules the same way.

Why Does It Matter?

If the data model is unclear, the same information may be repeated across tables, reports can become inconsistent, and migrations become harder as the application grows. Normalization choices, field ownership, and required relationships can be discussed on the ERD before code locks them in.

Business Use

In ERP integrations, CRM systems, inventory management, booking flows, and reporting projects, an ERD creates a shared language between developers, product owners, and business teams. A clear ERD speeds up SQL table design and reduces future data consistency problems.