What is Normalization in SQL?
Normalizing databases reduces redundancy, improves data consistency and simplifies query performance while simultaneously increasing storage space and query complexity. In this article we will look at what normalization is and its various forms, as well as why its importance.
Normalizing databases serves to reduce redundancy by isolating related information into separate tables. This ensures that each table only contains unique data, while each column relates directly to one other attribute in some way. Furthermore, normalization helps prevent problems when storing, updating or deleting information.
There are three stages to database normalization, known as First, Second and Third Normal Form. Each one builds upon the previous stage by eliminating redundant data while making sure all tables share one key.
1NF: To define it in first normal form, a relation must not contain any repeating groups and all attributes are single-valued; additionally it cannot include composite or multiple-valued attributes.
2NF: For a relation to be considered in second normal form it must meet all criteria set out by 1NF as well as have no partial dependencies between candidate keys and any partial dependency between columns in its table. Furthermore it should eliminate redundancies by grouping all distinct values into their own table while distancing relationships among columns within its same table.
3NF: To define third normal form (or 3NF), consider that any relation satisfying the criteria for two normal form and lacking transitive partial dependency can also be in third normal form. It eliminates redundancies by further segmenting unique values into their own table while eliminating relations from other tables via common key.
Fourth Normal Form (4NF): A relation is considered fourth normal form if it fulfills both 3NF criteria and does not rely on functional dependencies between fields, for instance when including city information with sales rep data in one row from sales table. To overcome this snag we would need to create two new tables with identical fields but individual rows for city and sales representative respectively in order to establish 4NF compliance.
Note that it can be challenging to reach all levels of normalization in practice; 3NF for instance requires numerous small tables which could compromise database performance and exceed file and memory capacities, while higher forms of normalization often aren’t practical in the real world. Therefore, finding a balance between database normalization and practicality is of utmost importance when creating efficient databases. Having an understanding of normalization principles is key in this regard.