In this post, I will explain the difference between Primary Key and Unique Key.
Primary Key and Unique Key provide uniqueness for a column or set of columns in a table. But there are different characteristics or behaviour of them, which makes Primary Key and Unique Key different. Please find below the difference between Primary Key and Unique Key :
Sr No | Primary Key | Unique Key |
1 | A database table can have only one Primary Key. | A database table can have more than one Unique Key. |
2 | Primary Key is not nullable (Doesn't allow NULL value). | Unique Key is nullable (Allows at least one NULL value). |
3 | Primary Key generates a Unique Clustered Index. | Unique Key generates a Unique Non-Clustered Index. |
4 | Primary Key is used to identify a row (a record) in a table. | Unique Key is used to prevent duplicate values in a column. |