DBMS Concepts

DBMS Tutorial Components of DBMS. Applications of DBMS The difference between file system and DBMS. Types of DBMS DBMS Architecture DBMS Schema Three Schema Architecture. DBMS Languages.

DBMS ER Model

ER model: Entity Relationship Diagram (ERD) Components of ER Model. DBMS Generalization, Specialization and Aggregation.

DBMS Relational Model

Codd’s rule of DBMS Relational DBMS concepts Relational Integrity Constraints DBMS keys Convert ER model into Relational model Difference between DBMS and RDBMS Relational Algebra DBMS Joins

DBMS Normalization

Functional Dependency Inference Rules Multivalued Dependency Normalization in DBMS: 1NF, 2NF, 3NF, BCNF and 4NF

DBMS Transaction

What is Transaction? States of transaction ACID Properties in DBMS Concurrent execution and its problems DBMS schedule DBMS Serializability Conflict Serializability View Serializability Deadlock in DBMS Concurrency control Protocols

Difference

Difference between DFD and ERD

Misc

Advantages of DBMS Disadvantages of DBMS Data Models in DBMS Relational Algebra in DBMS Cardinality in DBMS Entity in DBMS Attributes in DBMS Data Independence in DBMS Primary Key in DBMS Foreign Key in DBMS Candidate Key in DBMS Super Key in DBMS Aggregation in DBMS Hashing in DBMS Generalization in DBMS Specialization in DBMS View in DBMS File Organization in DBMS What Is A Cloud Database What Is A Database Levels Of Locking In DBMS What is RDBMS Fragmentation in Distributed DBMS What is Advanced Database Management System Data Abstraction in DBMS Checkpoint In DBMS B Tree in DBMS BCNF in DBMS Advantages of Threaded Binary Tree in DBMS Advantages of Database Management System in DBMS Enforcing Integrity Constraints in DBMS B-Tree Insertion in DBMS B+ Tree in DBMS Advantages of B-Tree in DBMS Types of Data Abstraction in DBMS Levels of Abstraction in DBMS 3- Tier Architecture in DBMS Anomalies in Database Management System Atomicity in Database Management System Characteristics of DBMS DBMS Examples Difference between Relational and Non-Relational Databases Domain Constraints in DBMS Entity and Entity set in DBMS ER Diagram for Banking System in DBMS ER Diagram for Company Database in DBMS ER Diagram for School Management System in DBMS ER Diagram for Student Management System in DBMS ER Diagram for University Database in DBMS ER Diagram of Company Database in DBMS Er Diagram Symbols and Notations in DBMS How to draw ER-Diagram in DBMS Integrity Constraints in DBMS Red-Black Tree Deletion in DBMS Red-Black Tree Properties in DBMS Red-Black Tree Visualization in DBMS Redundancy in Database Management System Secondary Key in DBMS Structure of DBMS 2-Tier Architecture in DBMS Advantages and Disadvantages of Binary Search Tree Closure of Functional Dependency in DBMS Consistency in Database Management System Durability in Database Management System ER Diagram for Bank Management System in DBMS ER Diagram for College Management System in DBMS ER Diagram for Hotel Management System in DBMS ER Diagram for Online Shopping ER Diagram for Railway Reservation System ER Diagram for Student Management System in DBMS Isolation in DBMS Lossless Join and Dependency Preserving Decomposition in DBMS Non-Key Attributes in DBMS Data Security Requirements in DBMS DBMS functions and Components What is Homogeneous Database? DBMS Functions and Components Advantages and Disadvantages of Distributed Database

Candidate Key in DBMS

Candidate key in DBMS: The candidate key is a single column or the set of columns that uniquely identifies the rows of data in the database table. It is a super key but with no repeated columns or attributes. So, this key is also called as minimal super key. Every table in the database must have at least a single candidate key.

Properties of Candidate key

Following are some of the properties of the candidate key:

  • A candidate may have more than one column or attribute.
  • The column, which is defined as the candidate key, will not contain any NULL value.
  • It uniquely identifies each row in the table of the database.
  • The values defined in the candidate key must be unique.
  • Those attributes or columns which visible in some candidate key are called as the prime attributes.

We are describing the candidate key using the following example, so you can easily understand it.

This example uses one table Employee, which contains three columns or fields or attributes. The name of these three columns is Employee_ID, Employee_Name, Employee_EmailID.

Employee_IDEmployee_NameEmployee_EmailID
201Anuj[email protected]
202Chetan[email protected]
203Lalit[email protected]
204Lakshman[email protected]
205Lalit[email protected]

Now, we have to identify all the super key present in the table. After then, we have to eliminate the super keys, which contain the columns with duplicate attributes.

All the super keys of the Employee table are as follows:  

1. { Employee_ID}: This column will contain all the unique values; hence this column can be used as a candidate key.

2. {Employee_EmailID}: As no two employees have the same emailID, hence Employee_EmailID column can be used as a candidate key.  

3. { Employee_ID, Employee_EmailID }: As both ID and EmailID is unique for all the employees, this column combination can be a candidate key.

4. { Employee_ID, Employee_Name }: This column combination cannot be used as a candidate key because the two employees may have the same name.

5. { Employee_ID, Employee_Name, Employee_EmailID }: This column combination cannot be used as a candidate key because the Employee_name column may have duplicate values.

6. { Employee_Name, Employee_EmailID }: This column combination cannot be used as a candidate key because the Employee_name column may have duplicate values.

So, after elimination, following are the columns which can be the candidate key of the employee table:

{ Employee_ID},

{Employee_EmailID}, and

{ Employee_ID, Employee_EmailID }