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

Primary Key vs. Unique Key Constraints in RDBMS

When it comes to relational database management systems (RDBMS), understanding the difference between primary key and unique key constraints is crucial for effective database design and data integrity.

Primary Key:

A primary key is a column or a set of columns that uniquely identify each record in a table. It must have a unique value for each row and cannot contain NULL values. The primary key is used to establish relationships between different tables and ensures data integrity within the database.

Unique Key:

A unique key constraint ensures that all values in a column or a set of columns are unique and different from all other values in the same column(s). Unlike the primary key, a unique key can contain NULL values, but only one NULL value is allowed. This constraint helps to enforce data integrity by preventing duplicate values within the table.

In summary, the main difference between primary key and unique key constraints in an RDBMS is that a primary key uniquely identifies each record and does not allow NULL values, while a unique key ensures uniqueness but can allow one NULL value.

For further insights into the distinctions between these two constraints and their impact on database management, refer to the expert analysis in this informative piece on "Primary Key vs Unique Key Constraints in RDBMS."