Database normalization คืออะไร?

❌ orders table with everything in one place — data is DUPLICATED:
  order_id | customer_name | customer_email | product | price
  1        | Ann           | [email protected]      | Phone   | 999
  2        | Ann           | [email protected]      | Case    | 20      ← Ann's info repeated!

Problems (anomalies):
  ✗ UPDATE anomaly — change Ann's email → must update EVERY one of her orders
  ✗ INSERT anomaly — can't add a customer without an order
  ✗ DELETE anomaly — deleting Ann's last order loses her info entirely
  ✗ Wasted storage and inconsistency risk