Why data in an RDBMS needs to be normalized ?

Normalsation is the process of analysing the given relation schemas based on their functional dependency and primary keys to achieve the desirable properties of minimising redundancy and minimising insertion, deletion and update anomalies. Unsatisfactory relation schemas that do not meet certain conditions (called normal form tests) are decomposed into smaller relations that meet the tests and hence possess the desirable property.

Through normalisation we can achieve the following benefits:

1. Minimise redundancy
2. Minimise insertion abnormalities
3. Minimise deletion abnormalities
4. Minimise update abnormalities

Consider a relation which contain employee details and departments. There are certain problems in this type of data base. If we want to insert a new department without employees it can cause difficulties. Normally employee identification number ( or social security number etc.) may be a key value. We cannot keep it null. But if we have separate employee and department tables then such a problem will not raise. New department can be inserted in the department table and new employee will be entered into employee table and they do not interfere with each other.

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