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MySQL Articles
Page 105 of 355
Fourth Normal Form (4NF)
What is 4NF?The 4NF comes after 1NF, 2NF, 3NF, and Boyce-Codd Normal Form. It was introduced by Ronald Fagin in 1977.To be in 4NF, a relation should be in Bouce-Codd Normal Form and may not contain more than one multi-valued attribute.ExampleLet us see an example −Movie_NameShooting_LocationListingMovieOneUKComedyMovieOneUKThrillerMovieTwoAustraliaActionMovieTwoAustraliaCrimeMovieThreeIndiaDramaThe above is not in 4NF, sinceMore than one movie can have the same listingMany shooting locations can have the same movieLet us convert the above table in 4NF −Movie_NameShooting_LocationMovieOneUKMovieOneUKMovieTwoAustraliaMovieTwoAustraliaMovieThreeIndiaMovie_NameListingMovieOneComedyMovieOneThrillerMovieTwoActionMovieTwoCrimeMovieThreeDramaNow the violation is removed and the tables are in 4NF.
Read MoreDomain-Key Normal Form
A relation is in DKNF when insertion or delete anomalies are not present in the database. Domain-Key Normal Form is the highest form of Normalization. The reason is that the insertion and updation anomalies are removed. The constraints are verified by the domain and key constraints.A table is in Domain-Key normal form only if it is in 4NF, 3NF and other normal forms. It is based on constraints −Domain ConstraintValues of an attribute had some set of values, for example, EmployeeID should be four digits long −EmpIDEmpNameEmpAge0921Tom330922Jack31Key ConstraintAn attribute or its combination is a candidate keyGeneral ConstraintPredicate on the set ...
Read MoreSecondary Key in RDBMS
What is a Secondary KeySecondary Key is the key that has not been selected to be the primary key. However, it is considered a candidate key for the primary key.Therefore, a candidate key not selected as a primary key is called secondary key. Candidate key is an attribute or set of attributes that you can consider as a Primary key.Note: Secondary Key is not a Foreign Key.ExampleLet us see an example −Student_IDStudent_EnrollStudent_NameStudent_AgeStudent_Email0969122717Manish25aaa@gmail.com0559122655Manan23abc@gmail.com0679122699Shreyas28pqr@gmail.comAbove, Student_ID, Student_Enroll and Student_Email are the candidate keys. They are considered candidate keys since they can uniquely identify the student record. Select any one of the candidate key as ...
Read MoreTransitive dependency in DBMS
What is Transitive DependencyWhen an indirect relationship causes functional dependency it is called Transitive Dependency.If P -> Q and Q -> R is true, then P-> R is a transitive dependency.To achieve 3NF, eliminate the Transitive Dependency.ExampleMovie_IDListing_IDListing_TypeDVD_Price ($)M08L09Crime180M03L05Drama250M05L09Crime180The above table is not in 3NF because it has a transitive functional dependency −Movie_ID -> Listing_IDListing_ID -> Listing_TypeTherefore, the following has transitive functional dependency.Movie_ID -> Listing_TypeThe above states the relation violates the 3rd Normal Form (3NF).To remove the violation, you need to split the tables and remove the transitive functional dependency.Movie_IDListing_IDDVD_Price ($)M08L09180M03L05250M05L09180Listing_IDListing_TypeL09CrimeL05DramaL09CrimeNow the above relation is in Third Normal Form (3NF) ...
Read MoreHow to identify entity from a given problem
Entity in DBMS can be a real-world object with an existence. To identify entity from a given problem, follow the below given tips −Under the problem description, try to find the entity.Search for nouns, like Teacher, Doctor, etc.Classify nouns to get a wider picture about the entities.Read the problem description repeatedly.Entities are like Persons, Students, Teachers, Courses.Entities has attributes, that properties describing it, for example, for Professor entity, the attributes are Professor_Name, Professor_Address, Professor_Salary, etcFor example, Problem DescriptionHospital has doctors and patients. Patients visit the hospital to get a consultation from the doctor. Doctor may suggest tests to examine the condition ...
Read MoreData Dictionary in DBMS
Data Dictionary consists of database metadata. It has records about objects in the database.What Data Dictionary consists ofData Dictionary consists of the following information −Name of the tables in the databaseConstraints of a table i.e. keys, relationships, etc.Columns of the tables that related to each otherOwner of the tableLast accessed information of the objectLast updated information of the objectAn example of Data Dictionary can be personal details of a student −ExampleStudent_IDStudent_NameStudent_AddressStudent_CityThe following is the data dictionary for the above fields −Types of Data DictionaryHere are the two types of data dictionary −Active Data DictionaryThe DBMS software manages the active data ...
Read MoreHow to normalize a Database Table
Normalization removes data redundancy and update, insert and delete anomalies and gives you a normalized perfect database design that a database administrator love.To normalize a database table, follow the below given steps that highlights the role of normalization forms and its uses −First Normal Form (1NF)1 INF is useful in removing the data redundancy issue and anomalies of a database. All attributes in 1NF should have atomic domains.Second Normal Form (2NF)The Second Normal Form eliminates partial dependencies on primary keys.Third Normal Form (3NF)The Third Normal Form eliminates Transitive Functional Dependency.Fourth Normal Form (4NF)To be in 4NF, a relation should may ...
Read MoreFifth Normal Form (5NF)
The 5NF (Fifth Normal Form) is also known as project-join normal form. A relation is in Fifth Normal Form (5NF), if it is in 4NF, and won’t have lossless decomposition into smaller tables.You can also consider that a relation is in 5NF, if the candidate key implies every join dependency in it.ExampleThe below relation violates the Fifth Normal Form (5NF) of Normalization −EmpNameEmpSkillsEmpJob (Assigned Work)DavidJavaE145JohnJavaScriptE146JamiejQueryE146EmmaJavaE147The above relation can be decomposed into the following three tables; therefore, it is not in 5NF −EmpNameEmpSkillsDavidJavaJohnJavaScriptJamiejQueryEmmaJavaThe following is the relation that displays the jobs assigned to each employee −EmpNameEmpJobDavidE145JohnE146JamieE146EmmaE147Here is the skills that are ...
Read MoreObjectives of a good Database Design
Good Database Design is what everyone wants to achieve to avoid the consequences of dealing with a bad design.The following are the objectives of a good database design −Avoid Redundant DataThe table in the database should be constructed following standards and with utmost dedication. It should have different fields and minimize redundant data. The table should always have a Primary Key that would be a unique id.Faultless InformationThe database should follow the standards and conventions and provide meaningful information useful to the organization.Data IntegrityIntegrity assists in guaranteeing that the values are valid and faultless. Data Integrity is set to tables, ...
Read MoreOne-to-One Relationship in DBMS
Relationships in DBMS can be stated as a relation between two entities like Employee-Department, Student-Course, etc.One-to-One relationship in DBMS is a relationship between an instance of an entity with another.The relation can be stated as −An Employee is issued an Employee ID Card. An individual employee is offered a unique ID card in the company. Here, Employee and ID Card (ID_Card) are entities.
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