Primary Key Constraint And Unique Constraint in SQL Server

Question

I want to know what is difference between primary key constraint and unique constraint in SQL Server. Thank you.

Satyapriya Nayak · Answer

Hi Vipendra Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column where are unique creates a nonclustered index by default. Another major difference is that primary key doesn't allow NULLs but unique key allows one NULL only. Thanks

Santhosh Kumar Jayaraman · Answer

Primary Key: 1.Clustered index.only one primary key per table. 2.Doesnt allow null. Unique key: 1.Non clustered index. you can have as many unique keys in a table. 2.Allows null