Normal Forms in SQL Server

First Normal Form (1NF)

First normal form (1NF) sets the very basic rules for an organized database:
• Eliminate duplicative columns from the same table.
• Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).

Second Normal Form (2NF)

Second normal form (2NF) further addresses the concept of removing duplicative data:
• Meet all the requirements of the first normal form.
• Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
• Create relationships between these new tables and their predecessors through use of foreign keys.

Third Normal Form (3NF)

Third normal form (3NF) goes one large step further:
• Meet all the requirements of the second normal form.
• Remove columns that are not dependent upon the primary key.

Fourth Normal Form (4NF)

Finally, fourth normal form (4NF) has one additional requirement:
• Meet all the requirements of the third normal form.
• A relation is in 4NF if it has no multi-valued dependencies.