Difference between Primary Key & Unique Key:-

Primary Key	Unique Key
Primary Key can't accept null values	Unique key can accept only one null value
By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index	By default, Unique key is a unique non-clustered index.
We can have only one Primary key in a table.	We can have multiple unique key in a table.
Primary key can be made foreign key into another table.	Unique key can not be made foreign key into another table.