Second normal form

2NFsecond
Second normal form (2NF) is a normal form used in database normalization.wikipedia
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Database normalization

normalizationnormalizednormal form
Second normal form (2NF) is a normal form used in database normalization.
Codd went on to define the second normal form (2NF) and third normal form (3NF) in 1971, and Codd and Raymond F. Boyce defined the Boyce-Codd normal form (BCNF) in 1974.

Third normal form

3NF3NF databasesthird
That is addressed in third normal form.
Requiring existence of "the key" ensures that the table is in 1NF; requiring that non-key attributes be dependent on "the whole key" ensures 2NF; further requiring that non-key attributes be dependent on "nothing but the key" ensures 3NF.

First normal form

1NF
It is worth noting that this design meets the additional requirements for second and third normal form.

Functional dependency

functional dependenciesfunctionally dependentinspired from relational database theory
A functional dependency on part of any candidate key is a violation of 2NF.

Primary key

Alternate keydefining database keykey
In addition to the primary key, the relation may contain other candidate keys; it is necessary to establish that no non-prime attributes have part-key dependencies on any of these candidate keys.

Attribute-value system

attributeattribute valuesattribute-value centric
*Attribute-value system

Fourth normal form

4NF4NF database normalization
Whereas the second, third, and Boyce–Codd normal forms are concerned with functional dependencies, 4NF is concerned with a more general type of dependency known as a multivalued dependency.

View (SQL)

viewviewsdatabase view
Without the use of views, the normalization of databases above second normal form would become much more difficult.

Boyce–Codd normal form

BCNFBoyce-Codd normal formBoyce Codd Normal Form
Recall that 2NF prohibits partial functional dependencies of non-prime attributes (i.e., an attribute that does not occur in any candidate key.