As you can see we have removed the partial functional dependency that we initially had. Now, in the table, the column Office Location is fully dependent on the primary key of that table, which is Department ID. Now that we have learnt 1st and 2nd normal forms lets head to the next part of this Normalization in SQL article. The other condition is there should be no transitive dependency for non-prime attributes. Now in order to achieve third normal form, we need to divide the table as shown below: As you can see from the above tables all the non-key attributes are now fully functional dependent only on the primary key.
|Published (Last):||5 January 2004|
|PDF File Size:||13.31 Mb|
|ePub File Size:||11.98 Mb|
|Price:||Free* [*Free Regsitration Required]|
For example, there are discussions even on 6th Normal Form. The evolution of Normalization theories is illustrated below- Database Normalization Example: We will study normalization with the help of a case study.
Assume, a video library maintains a database of movies rented out. Without any normalization, all information is stored in one table as shown below. Here you see Movies Rented column has multiple values. Each record needs to be unique. A KEY is a value used to identify a record in a table uniquely. A KEY could be a single column or combination of multiple columns Note: Columns in a table that are NOT used to identify a record uniquely are called non-key columns.
What is a Primary Key? A primary is a single column value used to identify a database record uniquely. It has following attributes A primary key cannot be NULL A primary key value must be unique The primary key values should rarely be changed The primary key must be given a value when a new record is inserted.
What is Composite Key? A composite key is a primary key composed of multiple columns used to identify a record uniquely In our database, we have two people with the same name Robert Phil, but they live in different places. Hence, we require both Full Name and Address to identify a record uniquely. That is a composite key. 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.
It helps connect your Tables A foreign key can have a different name from its primary key It ensures rows in one table have corresponding rows in another Unlike the Primary key, they do not have to be unique. Suppose, a novice inserts a record in Table B such as You 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. 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 change Consider the table 1.
Changing the non-key column Full Name may change Salutation. There are no transitive functional dependencies, and hence our table is in 3NF In Table 3 Salutation ID is primary key, and in Table 1 Salutation ID is foreign to primary key in Table 3 Now 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. Sometimes is BCNF is also referred as 3.
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.
Boyce-Codd Normal Form (BCNF)
FIRST NORMAL FORM It is a property of a relation in a relational database wherein only when the domain of each attribute has only atomic values values that cannot be divided or simplified further and the value of each attribute has only one value from the selected domain. Edgar Codd, an English Computer Scientist, stated that a relation is said to be in the first normal form when none of its domains have any sets as elements. It enforces several criteria including: 1 Removing repeating groups in individual tables, 2 Creating separate tables for every set of related data and 3 Identifying related data using the primary key of a given set. Example: Consider a table containing the details of a company. The fields to be included are employee name, employee ID no, employee location and employee contact no.
Normalization of Database
As you can see, we have also added some sample data to the table. In the table above: One student can enrol for multiple subjects. And, there can be multiple professors teaching one subject like we have for Java. What do you think should be the Primary Key? One more important point to note here is, one professor teaches only one subject, but one subject may have two different professors. Hence, there is a dependency between subject and professor here, where subject depends on the professor name. This table satisfies the 1st Normal form because all the values are atomic, column names are unique and all the values stored in a particular column are of same domain.
What is Normalization in SQL and what are its types?