Database Normal Forms
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.