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Guess how we’ll transform this into 3NF? That’s right we split the relation.

The candidate key is the part and supplier set, which is expressed like this, but the value of teacher date of birth is functionally dependent on teacher – a non-prime attribute.The underlined attributes are the candidate key. Let’s see an example of a relation that does not satisfy 2NF. Informally, the second normal form states that all attributes must depend on the entire candidate key. However, for a relation to be 2NF, the information stored by non-prime attributes must be related to the whole information in the candidate key. A non-prime attribute is an attribute that is not part of the candidate key.For a more detailed exploration of keys, see this article. It’s minimal in that if you removed one attribute, the remaining attributes do not form a candidate key. A candidate key is a minimal set of attributes that determines the other attributes included in the relation.Let’s go back to the idea of candidate keys and non-prime attributes. For more on functional dependencies, see this article. For example, your age is functionally dependent on your date of birth. What does this mean? If the value of attribute A is determined by the value of attribute S, then A is functionally dependent on S. In other words, any column that’s not a key column is dependent on the whole information in the candidate key. No non-prime attributes are functionally dependent on a subset of the candidate key(s).Second Normal Form (2NF)Ī relation is in second normal form (2NF) if and only if: If you’re interested in reading more about the first normal form, I recommend the article What Is the Actual Definition of First Normal Form? by my colleague Konrad Zdanowski. To transform this relation to the first normal form, we should store each course subject as a single value, so that each student-course assignment is a separate tuple: course subjects: databases as one element, mathematics as another), so it’s not an atomic value. This list can be broken down into smaller elements (i.e. Jane Smith is assigned to two courses (Databases and Mathematics), and they are stored in one field as a comma-separated list. This relation is not in 1NF because the courses attribute has multiple values.

Below is an example of a relation that does not satisfy 1NF criteria: In practice, 1NF means that you should not have lists or other composite structures as attribute values.

All attribute values are atomic, which means they can’t be broken down into anything smaller.

Each attribute contains only one value.

First Normal Form (1NF)Ī relation is in first normal form (1NF) if (and only if): The normalization process consists of modifying the design through different stages, going from an unnormalized set of relations (tables), to the first normal form, then to the second normal form, and then to the third normal form.ĭon’t worry if this sounds complicated I promise it will get clearer as we go through each step. So, what is this theory of normal forms? It deals with the mathematical construct of relations (which are a little bit different from relational database tables). There are normal forms higher than 3NF, but in practice you usually normalize your database to the third normal form or to the Boyce-Codd normal form, which we won’t cover here. In this article, we’ll review the most basic: The theory of normal forms gives rigorous meaning to these informal concepts.

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Basically, you want each piece of information to be stored exactly once if the information changes, you only have to update it in one place. Normalization in relational databases is a design process that minimizes data redundancy and avoids update anomalies. What is database normalization? What are the different normal forms, and what do they do? Find out in this article.