Normalization in MYSQL

What is normalization in MySQL and in which case and how we need to use it?

I try to attempt to explain normalization in layman terms here. First off, it is something that applies to relational database (Oracle, Access, MySQL) so it is not only for MySQL.

Normalisation is about making sure each table has the only minimal fields and to get rid of dependencies. Imagine you have an employee record, and each employee belongs to a department. If you store the department as a field along with the other data of the employee, you have a problem - what happens if a department is removed? You have to update all the department fields, and there's opportunity for error. And what if some employees does not have a department (newly assigned, perhaps?). Now there will be null values.

So the normalisation, in brief, is to avoid having fields that would be null, and making sure that the all the fields in the table only belong to one domain of data being described. For example, in the employee table, the fields could be id, name, social security number, but those three fields have nothing to do with the department. Only employee id describes which department the employee belongs to. So this implies that which department an employee is in should be in another table.

Here's a simple normalization process.

EMPLOYEE ( < employee_id >, name, social_security, department_name)

This is not normalized, as explained. A normalized form could look like

EMPLOYEE ( < employee_id >, name, social_security)

Here, the Employee table is only responsible for one set of data. So where do we store which department the employee belongs to? In another table

EMPLOYEE_DEPARTMENT ( < employee_id >, department_name )

This is not optimal. What if the department name changes? (it happens in the US government all the time). Hence it is better to do this

EMPLOYEE_DEPARTMENT ( < employee_id >, department_id )
DEPARTMENT ( < department_id >, department_name )

There are first normal form, second normal form and third normal form. But unless you are studying a DB course, I usually just go for the most normalized form I could understand.

Hope this helps.

Normalization is not for MYSql only. Its a general database concept.

Normalization is the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.

Normal forms in SQL are given below.

First Normal form (1NF): A relation is said to be in 1NF if it has only single valued attributes, neither repeating nor arrays are permitted.

Second Normal Form (2NF): A relation is said to be in 2NF if it is in 1NF and every non key attribute is fully functional dependent on the primary key.

Third Normal Form (3NF): We say that a relation is in 3NF if it is in 2NF and has no transitive dependencies.

Boyce-Codd Normal Form (BCNF): A relation is said to be in BCNF if and only if every determinant in the relation is a candidate key.

Fourth Normal Form (4NF): A relation is said to be in 4NF if it is in BCNF and contains no multivalued dependency.

Fifth Normal Form (5NF): A relation is said to be in 5NF if and only if every join dependency in relation is implied by the candidate keys of relation.

Domain-Key Normal Form (DKNF): We say that a relation is in DKNF if it is free of all modification anomalies. Insertion, Deletion, and update anomalies come under modification anomalies

Seel also

Database Normalization Basics