The grain describes what one row represents. Primary and foreign keys identify records and relationships, while consistent grain prevents accidental double counting.

Worked example

orders(order_id, customer_id, ordered_at)
order_items(order_id, line_number, product_id, quantity)

Put it into practice

Define the grain and candidate keys of orders, order items, products, and customers.

Check your understanding

• Explain the main idea in your own words.
• Compare your result with the worked example and identify any assumptions you made.
• Record one question or edge case to discuss with your instructor.

Connect this to your project

Build a repeatable retail analytics pipeline with staging tables, a sales fact table, and documented quality checks.

Keep the output of this activity in your project folder. You will use it when you review and present your final work.