Unlocking the Power of Keys in DBMS: A Comprehensive Guide – Part 2

“Decoding the Keys in DBMS: A visual guide to understanding the different types of keys in Database Management Systems.”

A key in DBMS is an attribute or a set of attributes that help to uniquely identify a tuple (or row) in a relation (or table). They are also used to establish and identify relationships between tables.

Types of Keys in DBMS

There are several types of keys in DBMS, each with its unique characteristics and use cases:

Primary Key

A primary key is the first key used to identify one and only one instance of an entity uniquely. For example, consider a table named ‘Students’ with columns ‘StudentID’, ‘Name’, and ‘Age’. Here, ‘StudentID’ could be a primary key as it can uniquely identify each student in the table.

SQL sample code.

CREATE TABLE Students (
    StudentID int PRIMARY KEY,
    Name varchar(255) NOT NULL,
    Age int
);

Candidate Key

A candidate key is an attribute or set of attributes that can uniquely identify a tuple. For instance, in a table named ‘Employees’ with columns ‘EmployeeID’, ‘Name’, and ‘Email’, both ‘EmployeeID’ and ‘Email’ could be candidate keys as they can uniquely identify each employee.

SQL sample code.

CREATE TABLE Employees (
    EmployeeID int,
    Name varchar(255) NOT NULL,
    Email varchar(255) UNIQUE
);

Super Key

A super key is an attribute set that can uniquely identify a tuple1. It is a set of one or more columns that can uniquely identify a record in a table. For example, in a ‘Customers’ table, a combination of ‘CustomerID’ and ‘Email’ could be a super key.

Foreign Key

Foreign keys are the columns of a table used to point to the primary key of another table1. They act as a cross-reference between tables. For example, in an ‘Orders’ table, a ‘CustomerID’ column could be a foreign key that points to the ‘CustomerID’ column in a ‘Customers’ table.

SQL sample code.

CREATE TABLE Orders (
    OrderID int PRIMARY KEY,
    ProductName varchar(255) NOT NULL,
    CustomerID int,
    FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

Alternate Key

An alternate key is any candidate key which is not a primary key1. For example, in the ‘Employees’ table mentioned above, if ‘EmployeeID’ is the primary key, then ‘Email’ becomes an alternate key.

SQL sample code.

CREATE TABLE Employees (
    EmployeeID int PRIMARY KEY,
    Name varchar(255) NOT NULL,
    Email varchar(255) UNIQUE
);

In conclusion, understanding the different types of keys in DBMS is crucial for anyone working with databases. They not only ensure data integrity but also facilitate efficient data retrieval and manipulation.

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