What is the difference between a primary key and a unique key in a database management system (DBMS)?

Primary Key vs. Unique Key in a Database Management System (DBMS)

When it comes to database management systems (DBMS), understanding the difference between a primary key and a unique key is crucial. Both primary keys and unique keys are used to enforce data integrity and ensure the uniqueness of values in a database table. However, there are some key differences between the two:

Primary Key:

• A primary key is a column or a set of columns that uniquely identifies each record in a table.
• A primary key column cannot contain NULL values, and each value must be unique within the table.
• There can be only one primary key in a table, and it is used as the default clustering key for the table.

Unique Key:

• A unique key is a constraint that ensures the uniqueness of values in a column or a set of columns.
• Unlike a primary key, a unique key can contain NULL values, but each non-NULL value must be unique within the table.
• There can be multiple unique keys in a table, and they are used to enforce the uniqueness of values other than the primary key.

In summary, while both primary keys and unique keys serve the purpose of maintaining data integrity, primary keys uniquely identify each record in a table and are used for clustering, whereas unique keys ensure the uniqueness of values within a column or set of columns, allowing for NULL values.

Conclusion:

Understanding the distinction between primary keys and unique keys in a DBMS is essential for designing efficient and well-structured database schemas that comply with data integrity requirements.