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What is Normalization?Normalization is a database design technique which organizes tables in a manner that reduces redundancy and dependency of data.It divides larger tables to smaller tables and links them using relationships.In this tutorial, you will learn-.The inventor of the relational model Edgar Codd proposed the theory of normalization with the introduction of First Normal Form, and he continued to extend theory with Second and Third Normal Form. Later he joined with Raymond F. Boyce to develop the theory of Boyce-Codd Normal Form.Theory of Data Normalization in SQL is still being developed further. For example, there are discussions even on 6 th Normal Form. However, in most practical applications, normalization achieves its best in 3 rd Normal Form. The evolution of Normalization theories is illustrated below. Before we proceed let's understand a few things - What is a KEY?A KEY is a value used to identify a record in a table uniquely.
Hence, we require both Full Name and Address to identify a record uniquely. That is a composite key.Let's move into second normal form 2NF 2NF (Second Normal Form) Rules. Rule 1- Be in 1NF. Rule 2- Single Column Primary KeyIt is clear that we can't move forward to make our simple database in 2 nd Normalization form unless we partition the table above.We have divided our 1NF table into two tables viz. Table 1 and Table2.
Table 1 contains member information. Table 2 contains information on movies rented.We have introduced a new column called Membershipid which is the primary key for table 1. Records can be uniquely identified in Table 1 using membership id Database - Foreign KeyIn Table 2, MembershipID is the Foreign KeyForeign Key references the primary key of another Table! It helps connect your Tables. A foreign key can have a different name from its primary key.
Pierrot dictators circus rar files. It ensures rows in one table have corresponding rows in another. Unlike the Primary key, they do not have to be unique. Most often they aren't.
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Foreign keys can be null even though primary keys can notWhy do you need a foreign key?Suppose, a novice inserts a record in Table B such asYou will only be able to insert values into your foreign key that exist in the unique key in the parent table. This helps in referential integrity.The above problem can be overcome by declaring membership id from Table2 as foreign key of membership id from Table1Now, if somebody tries to insert a value in the membership id field that does not exist in the parent table, an error will be shown! What are transitive functional dependencies?A transitive functional dependency is when changing a non-key column, might cause any of the other non-key columns to changeConsider the table 1. Changing the non-key column Full Name may change Salutation.Let's move into 3NF 3NF (Third Normal Form) Rules. Rule 1- Be in 2NF.
Rule 2- Has no transitive functional dependenciesTo move our 2NF table into 3NF, we again need to again divide our table. We have again divided our tables and created a new table which stores Salutations.There are no transitive functional dependencies, and hence our table is in 3NFIn Table 3 Salutation ID is primary key, and in Table 1 Salutation ID is foreign to primary key in Table 3Now our little example is at a level that cannot further be decomposed to attain higher forms of normalization. In fact, it is already in higher normalization forms. Separate efforts for moving into next levels of normalizing data are normally needed in complex databases.
However, we will be discussing next levels of normalizations in brief in the following. Even when a database is in 3 rd Normal Form, still there would be anomalies resulted if it has more than one Candidate Key.Sometimes is BCNF is also referred as 3.5 Normal Form. 4NF (Fourth Normal Form) RulesIf no database table instance contains two or more, independent and multivalued data describing the relevant entity, then it is in 4 th Normal Form. 5NF (Fifth Normal Form) RulesA table is in 5 th Normal Form only if it is in 4NF and it cannot be decomposed into any number of smaller tables without loss of data.
6NF (Sixth Normal Form) Proposed6 th Normal Form is not standardized, yet however, it is being discussed by database experts for some time. Hopefully, we would have a clear & standardized definition for 6 th Normal Form in the near future.That's all to Normalization!!! Summary. Database designing is critical to the successful implementation of a database management system that meets the data requirements of an enterprise system. Normalization helps produce database systems that are cost-effective and have better security models. Functional dependencies are a very important component of the normalize data process. Most database systems are normalized database up to the third normal forms.
A primary key uniquely identifies are record in a Table and cannot be null. A foreign key helps connect table and references a primary key.