Database manamement system_keys_sheikh_monirul_hasan
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The presentation discusses the five types of keys in Database Management Systems (DBMS): primary key, unique key, super key, candidate key, and foreign key, each with distinct functionalities and properties. It provides examples illustrating how these keys are used to uniquely identify records within a database. Additionally, it touches on composite keys that arise from combining two or more columns to create a unique identifier.
Database manamement system_keys_sheikh_monirul_hasan
- 1. Welcome to my Presentation Submitted by : Sheikh Monirul Hasan Id: 162015077 Department: CSE Green University of Bangladesh Submitted to : Biplob Chandra Debnath Lecturer : CSE 1
- 2. • DBMS has Five types of Keys in it and they all has different functionality. • The Keys are as follows: • Primary Key • Unique Key • Super Key • Candidate Key • Foreign Key Let’s discuss one by one all of the five keys with example. Presentation topic – DBMS Keys 2
- 3. PRIMARY KEY The Primary Key is an attribute or a set of attributes that uniquely identify a specific instance of an entity. Every entity in the data model must have a primary key whose values uniquely identify instances of the entity. 3
- 4. PRIMARY KEY Properties Of Primary Keys To qualify as a primary key for an entity, an attribute must have the following properties: It must have a non-null value for each instance of the entity The value must be unique for each instance of an entity The values must not change or become null during the life of each entity instance 4
- 5. PRIMARY KEY Example : Roll_NO Name Address 1 Sheikh Monirul Hasan Mirpur, Dhaka , Bangladesh 2 Sakib Mohakhali 3 Safa shawrapara 5
- 6. Unique Key Unique key Unique key is one or more column in a table used to uniquely identify each row in the table . It can contain NULL value. Example: student table : Uu Roll_No Name Address 1 Arafat Mirpur - Mission Dhanmondi 3 Safa Shawrapara 6
- 7. SUPER KEY Super Key is a set of attributes whose set of values can uniquely identify an entity instance in the entity set. A Super Key can contains one or more than one attributes. Super Key is the broadest definition of unique identifiers of an entity in an entity set. 7
- 8. Super Key Example : Roll_No Name Address 1 Arafat Mirpur 2 Mission Dhanmondi 3 Safa Shawrapara {Roll_No}, {Roll_No,Name} , {Roll_No,Adderss}, {Roll_No, Name, Address} all these sets are super key. 8
- 9. CANDIDATE KEY Candidate key is a set of one or more attributes whose set of values can uniquely identify an entity instance in the entity set. Any attribute in the candidate key cannot be omitted without destroying the uniqueness property of the Candidate key. It is minimal Super Key. 9
- 10. CANDIDATE KEY Example: Roll_No Name Phone_No City 121 Anik 765368 Jamalpur 451 Jakir 982312 Magura 762 Ridoy 095421 Faridpur 876 Mokles 532134 Manikgonj {Roll_No}, {Phone-No} are two candidate key. Because we can consider any one of these as a primary key . 10
- 11. FOREIGN KEY A Foreign key is an attribute that completes a relationship by identifying the parent entity. Foreign keys provide a method for maintaining integrity in the data (called referential integrity) and for navigating between different instances of an entity. Every relationship in the model must be supported by a foreign key. 11
- 12. Foreign Key Example : Roll_No Name Address 162015040 Arafat Mirpur 162015029 Mission Dhanmondi 162015015 Safa Shawrapara Roll_No Semester Marks 162015040 III 80 162015029 V 70 162015015 VII 75 Here Roll_No of marks table is foreign key. Student table : Marks table : 12
- 13. COMPOSITE KEY When a primary key is created from a combination of 2 or more columns, the primary key is called a composite key. Each column may not be unique by itself within the database table but when combined with the other column(s) in the composite key, the combination is unique. 13
- 15. 15 For the more information you can check out Sheikh Monirul Hasan Connect with me in social media Facebook LinkedIn Twitter
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