Database Normal Forms

Bulruno
1 min readMay 12, 2021

Primary Key: A single column value used to identify a database record uniquely. (It cannot be null, value must be unique, should rarely be changed, given a value when new record is inserted).

Composite Key: A composite key is a primary key composed of multiple columns used to identify a record uniquely.

Foreign Key: It references the primary key of another table. It helps to connect your tables.

Transitive functional dependencies: A transitive functional dependency is when changing a non-key column, might cause any of other non-key columns to change.

Super Key: Is a set of attributes within a table whose values can be used to uniquely identify a tuple. A candidate key is a minimal set of attributes necessary to identify a tuple, this is also called a minimal super key.

  • 1NF (First Normal Form)
  • 2NF (Second Normal Form)
  • 3NF (Third Normal Form)
  • BCNF (Boyce-Codd Normal Form)

1NF(First Normal Form):

  • Each column should contain single value
  • Each record needs to be unique

2NF(Second Normal Form):

Rule 1: Be in 1NF

Rule 2: Single column primary key

3NF(Third Normal Form):

Rule 1: Be in 2NF

Rule 2: Has no transitive functional dependencies.

BCNF(Boyce-Codd Normal Form):

Even when a database is in 3rd Normal Form, still there would be anomalies resulted if it has more than one candidate key.

4NF(Fourth Normal Form):

If no database table instance contains two or more, independent and multivalued data describing the relevant entity, then it is in 4th Normal Form.

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