In database management, keys are used to uniquely identify a record or row in a table. There are several types of keys in DBMS, each with its unique characteristics and uses. In this blog, we'll explore the different types of DBMS keys and provide examples of their use.

Primary Key

A primary key is a unique identifier for a record in a table. It must have a unique value for each row in the table and cannot be null. The primary key is used to enforce data integrity and is often used as a foreign key in other tables.

For example, let's say we have a table called "Customers" with the following columns: CustomerID, FirstName, LastName, and Email. In this case, we could use the CustomerID column as the primary key since it uniquely identifies each customer.

CREATE TABLE Customers (
CustomerID INT NOT NULL PRIMARY KEY,
FirstName VARCHAR(50),
LastName VARCHAR(50),
Email VARCHAR(100)
);

Foreign Key

A foreign key is a column in a table that refers to the primary key of another table. It is used to establish relationships between tables and ensure data consistency. A foreign key can be null, and it does not have to be unique.

For example, let's say we have another table called "Orders" with the following columns: OrderID, CustomerID, OrderDate, and TotalAmount. In this case, the CustomerID column would be a foreign key since it refers to the CustomerID column in the "Customers" table.

CREATE TABLE Orders (
OrderID INT NOT NULL PRIMARY KEY,
CustomerID INT,
OrderDate DATE,
TotalAmount DECIMAL(10,2),
FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

Super Key

A superkey is a set of one or more columns in a table that uniquely identifies each row in the table. A superkey can have extra attributes that are not necessary for uniqueness. All primary keys are superkeys, but not all superkeys are primary keys.

For example, let's say we have a table called "Students" with the following columns: StudentID, FirstName, LastName, Address, City, State, and ZipCode. In this case, a superkey could be the combination of StudentID and ZipCode since it uniquely identifies each student.

Candidate Key

A candidate key is a superkey that does not have any unnecessary attributes. In other words, it is the minimum set of columns that uniquely identifies each row in a table. A table can have multiple candidate keys.

For example, in the "Students" table, both StudentID and ZipCode are candidate keys since they each uniquely identify each student, and there are no extra attributes that are not necessary for uniqueness.

In conclusion, understanding the different types of DBMS keys is essential for effective database management. Primary keys are used to enforce data integrity, foreign keys establish relationships between tables, superkeys uniquely identify each row in a table, and candidate keys are the minimum set of columns that uniquely identify each row. By using these keys appropriately, you can ensure data consistency and integrity in your database.