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Relational Database and Normalization

Denormalization. SummaryDenormalization. Summary


Denormalization is a process of abandoning normal forms. This can be applied to optimize the database for specific needs. Normalization, but just the opposite.


There are 8 normal forms (6+2):

  • First Normal Form (1NF)
  • Second Normal Form (2NF)
  • Third Normal Form (3NF)
  • Boyce-Codd Normal Form (BCNF)
  • Fourth Normal Form (4NF)
  • Fifth Normal Form (5NF)
  • Domain-Key Normal Form (DKNF)
  • Sixth Normal Form (6NF)


We have considered four normal forms because the others are rarely used.


First normal formSecond normal formThird normal form
Every table should have a unique primary key (ID is usually used)Requires the First Normal FormRequires the Second Normal Form
Each attribute must have only one value, not multiple valuesThe data that repeatedly appear in several rows should be presented in separate tablesAll attributes that do not belong to the primary key, but belong to another attribute, should be placed in a separate table


Usually, the Third Normal Form is already in the Boyce-Codd Normal Form.

Conditions when Boyce-Codd NF is not in Third NF:

  • A relation has 2 or more primary/foreign keys.
  • These primary/foreign keys contain more than one attribute (composite keys).
  • These primary/foreign keys overlap, meaning they share at least one attribute.
1. What is normalization?
2. What are normal forms?
3. What is denormalization?


What is normalization?

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What are normal forms?

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What is denormalization?

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Section 3.

Chapter 6