Primary Key vs Unique Key in a Database

In a database, a primary key and a unique key are both used to uniquely identify records, but there are 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.
• There can be only one primary key in a table.
• Primary key columns cannot contain NULL values.
• Primary keys are used as foreign keys in other tables to establish relationships between tables.

Unique Key:

• A unique key also ensures the uniqueness of values in a column or set of columns.
• Unlike a primary key, a table can have multiple unique keys.
• Unique key columns can contain NULL values, but only one NULL value is allowed.
• Unique keys are used to enforce data integrity and prevent duplicate entries in a table.

So, in summary, while both primary keys and unique keys ensure data uniqueness, the main differences lie in their constraints and usage within a database schema.