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Normalization is the method used to optimize databases. It is important to implement a reasonable level of normalization by creating more tables that contain fewer columns and by defining a relationship between the tables. Normalizing a logical database design involves the use of formal methods to separate the data into multiple, related tables. These methods are called normalization rules. There are six different types of normalization forms, which are 1NF, 2NF, 3NF, 4NF, 5NF, and 6NF:

1. First Normal Form: First normal form (1NF) exists when all the columns in a table are atomic i.e., only a single value is allowed in each column. Also, there should not be a group value like more than one phone number in a phone number column. If a table violates the first normal rule, following steps should be taken to normalize the database: To make a column atomic, divide them into multiple columns. If there is group value, create separate tables for the column and relate the new table with a foreign key.
2. Second Normal Form: Second normal form (2NF) is used in database normalization. A table that is in first normal form must meet additional criteria if it is to qualify for second normal form. Specifically, a 1NF table is in 2NF if and only if, given any candidate key and any attribute that is not a constituent of a candidate key, the non-key attribute depends upon the whole of the candidate key rather than just a part of it.
3. Third Normal Form: The third normal form (3NF) is a normal form used in database normalization. 3NF was originally defined by E.F. Codd in 1971. Codd’s definition states that a table is in 3NF if and only if both of the following conditions hold: The relation R (table) is in second normal form (2NF). Every non-prime attribute of R is non-transitively dependent (i.e. directly dependent) on every key of R. A non-prime attribute of R is an attribute that does not belong to any candidate key of R. A transitive dependency is a functional dependency in which X -> Z (X determines Z) indirectly, by virtue of X -> Y and Y -> Z (where it is not the case that Y -> X). A 3NF definition that is equivalent to Codd’s, but expressed differently, was given by Carlo Zaniolo in 1982. This definition states that a table is in 3NF if and only if, for each of its functional dependencies X -> A, at least one of the following conditions holds: X contains A (that is, X -> A is trivial functional dependency), or X is a superkey, or A is a prime attribute (i.e., A is contained within a candidate key)
   • Boyce-Codd Normal Form: Boyce-Codd normal form (or BCNF) is a normal form used in database normalization. It is a slightly stronger version of the third normal form (3NF). A table is in Boyce-Codd normal form if and only if, for every one of its non-trivial functional dependencies X -> Y, X is a superkey – that is, X is either a candidate key or a superset thereof.
4. Fourth Normal Form: Fourth normal form (4NF) is a normal form used in database normalization. Introduced by Ronald Fagin in 1977, 4NF is the next level of normalization after Boyce-Codd normal form (BCNF). 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. Symbolically, it can be represented as follows: If A -> > B|C, then A -> B and A -> C. Here, A, B, and C are attributes.
5. Fifth Normal Form: Fifth normal form (5NF), also known as Project-join normal form (PJ/NF), is a level of database normalization designed to reduce redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships. A table is said to be in 5NF if and only if every join dependency in it is implied by the candidate keys.
6. Sixth Normal Form: Sixth normal form (6NF) is used in database normalization. A relation (table) is in sixth normal form if and only if it satisfies no nontrivial join dependencies at all. A join dependency is trivial if and only if at least one of the projections involved is taken over the set of all attributes of the relation (table) concerned.

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