What problem does normalisation solve?
It removes repeated data across many rows and prevents inconsistencies.
Normalisation is essential for maintaining data integrity in databases.
Why is repeating customer addresses a problem?
If the customer moves house, the address must be changed everywhere → causes errors.
This can lead to outdated or incorrect information in the database.
Why is repeating product name & price a problem?
Any change must be updated in every row → leads to inconsistent data.
This can result in discrepancies in product information across the database.
How does normalisation fix these issues?
By splitting data into focused tables linked by IDs.
This approach minimizes redundancy and enhances data integrity.
What is the core idea of normalisation?
Each fact is stored in one place only.
This principle helps to avoid data duplication.
What do other tables store instead of repeating data?
ID references (foreign keys).
Foreign keys maintain relationships between tables.
What is the typical goal of normalisation in real systems?
Reach Third Normal Form (3NF).
3NF is a standard for reducing redundancy and dependency.
What does 1NF stand for?
First Normal Form.
1NF is the initial step in the normalisation process.
What does 1NF require?
Each cell has one value only (atomic values).
This ensures that data is stored in its simplest form.
What is a violation of 1NF?
“Laptop, Headphones” stored in one cell.
This violates the atomicity requirement of 1NF.
Why is 1NF important?
Prevents junk cells, makes filtering and counting easy.
This improves the overall efficiency of data handling.
When does 2NF matter?
Only when the primary key is composite.
2NF addresses issues that arise from composite keys.
What is the rule of 2NF?
No partial dependencies — every non-key column must depend on the whole key.
This ensures that all attributes are fully functionally dependent on the primary key.
What is a partial dependency?
A column depends on only part of the composite key.
This can lead to redundancy and inconsistency.
Example of fixing 2NF?
Split Products, Orders, and OrderDetails into separate tables.
This helps eliminate partial dependencies.
Key benefit of reaching 2NF?
Product prices are stored once — no repeated product info.
This reduces redundancy and potential errors.
What is the rule of 3NF?
No transitive dependencies.
This ensures that non-key attributes are not dependent on other non-key attributes.
What is a transitive dependency?
A non-key column depends on another non-key column (not the primary key).
This can lead to unnecessary data duplication.
Example of a 3NF violation?
Orders table storing CustomerName and CustomerAddress.
This violates the principle of 3NF by having non-key attributes depend on each other.
How do you fix a 3NF violation?
Move customer details into a Customers table.
This separates the data into appropriate tables.
Key benefit of 3NF?
Only update customer address in one place.
This enhances data integrity and reduces maintenance effort.
Why is normalisation useful in real systems?
Gives clean data, fewer errors, easier reporting.
This improves the overall quality of data management.
What is the rule of thumb?
Aim for 3NF, then denormalise only if needed for performance.
This approach balances data integrity with performance needs.
What is over-normalisation?
Splitting info (like address) into too many tiny tables → unnecessary joins.
This can complicate queries and reduce performance.
